Interlayer Space Of Smectite Research Articles

Kinetics of phosphate adsorption from aqueous solution into organobentonite by cationic polymer grafted bentonite

Natural clays are abundantly available low-cost natural resource which is nontoxic to ecosystem. Over the recent years, research on the modification of clay to increase their adsorbent capacity to remove contaminants from aqueous solution. In this study, natural bentonite was modified with polydimethyldiallil tetraammonium chloride (PDMDMAC) and Hexadecyltrimethylammonium bromide (HDTMAB). Bentonite, PDMDMA-Bt and HDTMA-Bt were then characterized using XRD, XRF, SEM, FT-IR, elemental analysis and Brunauer-Emmett-Teller (BET) surface area techniques. The HDTMA+ and PDMDMA+ cations were found to be located on the surface and enters the interlayer spaces of smectite according to the XRD and SEM results. FT-IR spectra indicated the existence of HDTMA PDMDMA functional groups on the bentonite surface. The BET surface area significantly decreased after the modification due to the coverage of the pores of natural bentonite. After the characterization, the kinetics adsorption of phosphate ions (PO4-3) onto betonies, HDTMAB-Bt and PDMDMA-Bt was investigated. On kinetic data representation, pseudo-first, pseudo-second order and intraparticle diffusion models were used, with the pseudo-second-order model gave better correlation which indicates chemisorption between adsorbent and adsorbate molecules.

Adsorption of Pharmaceuticals onto Smectite Clay Minerals: A Combined Experimental and Theoretical Study

The adsorption of two pharmaceuticals, carbamazepine and paracetamol, onto the expandable clay mineral saponite has been studied through the combination of kinetic experiments, X-ray diffraction, and theoretical modeling. Kinetic experiments indicate low adsorption for carbamazepine and paracetamol on expandable smectite clay. Accordingly, X-ray diffraction experiments show that neither compound enters smectite interlayer space. Molecular dynamics simulations were carried out to understand the interactions between the two pharmaceuticals and the saponite basal surface in the presence of Na+ cations. Calculations reveal that paracetamol almost does not coordinate solution cations, whereas a rather low coordination to cation is observed for carbamazepine. As a result, the adsorption onto the clay surface results mainly from van der Waals interactions for both pharmaceuticals. Carbamazepine does adsorb the surface via two configurations, one involving cation coordination, which corresponds to a rather stable adsorption compared to paracetamol. This is confirmed by structural analyses completed with desorption free energy profile.

Smectite clay minerals reduce the acute toxicity of quaternary alkylammonium compounds towards potentially pathogenic bacterial taxa present in manure and soil

Quaternary alkylammonium compounds (QAACs) are a group of cationic surfactants which are disinfectants with numerous industrial and agricultural applications and frequently released into the environment. One recent hypothesis is that bacteria present in soil will be protected from acute toxic effects of QAACs in the presence of expandable layer silicates due to interlayer sorption. We therefore studied bacterial growth kinetics with high temporal resolution and determined minimal inhibitory concentrations (MICs) of two QAACs, benzyldimethyldodecylammonium chloride (BAC-C12) and didecyldimethylammonium chlorid (DADMAC-C10), for eight strains of different bacterial taxa (Escherichia coli, Acinetobacter, Enterococcus faecium, Enterococcus faecalis, and Pseudomonas fluorescens) in relation to QAAC sorption to smectite and kaolinite. The MICs of BAC-C12 and DADMAC-C10 were in the absence of smectite and kaolinite in the order of 10 to 30 µg mL−1 and 1.0 to 3.5 µg mL−1 for all strains except the more sensitive Acinetobacter strain. For all tested strains and both tested QAACs, the presence of smectite increased apparent MIC values while kaolinite had no effect on MICs. Sorption curves without bacteria showed that smectite sorbed larger amounts of QAACs than kaolinite. Correcting nominal QAAC concentrations employed in toxicity tests for QAAC sorption using the sorption curves explained well the observed shifts in apparent MICs. Transmission electron microscopy (TEM) demonstrated that the interlayer space of smectite expanded from 13.7 ± 1 Å to 19.9 ± 1.5 Å after addition of BAC-C12. This study provides first evidence that low charge 2:1 expandable layer silicates can play an important role for buffering QAAC toxicity in soils.

Coupling between clay swelling/collapse and cationic partition

The semipermeability of clay aggregates in mudstones, shales, and marine sediments gives rise to geological ultrafiltration of ions and water. This behavior has been numerically analyzed based on the theory of the electric double layer (EDL). The model of EDL is suited for describing ionic partitions in clay pore with a width of a few nanometers. However, the interlayer space of smectite might be hardly described by the EDL model. An explicit atomic-scale description is more appropriate for the interlayer space. Besides, clay swelling or collapse corresponding to a variation of environmental conditions, and its impact on partitions of water and ions between interlayers and environment, have not been taken into account numerically. With atomic-scale molecular dynamics simulations and thermodynamic integrations based on them, the coupling between montmorillonite swelling/collapse and partitions of water and cations under different aqueous activity conditions is systematically disclosed here. With the combination of the Horinek’s force field to describe cations and ClayFF force field for atoms in solid layers, consistent swelling/collapse of Na- and K-montmorillonite with experimental observations as a function of water activity is shown. The swelling/collapse is connected to the transition between monolayer and bilayer hydration states. Decomposition of the swelling/collapse free energy shows both energy and entropy contributions are important in determining the thermodynamically stable hydration state. Taking environmental water activity and Na+/K+ ionic activity ratio as variables, a picture of cationic partition in response to those variables is established. It shows, under all circumstances, K+ ions are enriched in montmorillonite, which might explain K+ depletion in pore fluids of sediments. A low water activity improves K+ enrichment in montmorillonite. In addition, cationic partition accompanies variations of hydration states and alters the ionic concentration of the aqueous environment. These results can be applied to explain water and ionic partitions during subsurface water flow and the diagenesis processes of sediments.

Molecular dynamics simulations of interactions of organic molecules found in oil with smectite: Influence of brine chemistry on oil recovery

The study is aimed at employing molecular dynamics simulations to study the interactions between smectite and major oil constituents, along with the impact of different brine chemistry (type of cation in a solution) and ionic strength on the compound mobility in fine pores.Clay minerals with smectitic type of mineral outer surface (smectite, illite-smectite, illite) are major constituents in many unconventional oil and gas reservoirs. Therefore, smectite was used as a model compound to test interactions of oil compounds with mineral surfaces. Natural crude oil is a complex mixture, which - for the purpose of simulating an influence of surrounding fluid on its interactions with smectite surfaces - needs to be simplified. The following molecules were selected as organic model compounds: decane, quinolone, nonanoic acid, benzamide, and heptylamine. Various protonation states were considered.The first two sets of simulations showed remarkably different interactions of the selected organic molecules with the smectite surface. In the first one, three water/oil coverage models of the surface were considered. In the second one, two different pore sizes were taken into account: 3 nm and 5 nm. Significant differences were readably visible between polar and non-polar organic molecules. Also, the degree of protonation was found to be a crucial factor affecting the molecules’ affinity to the mineral surface. The molecules that are well soluble in cyclohexane (here representing crude hydrocarbons phase) formed droplets in the water phase, whereas organic compounds miscible in water were concentrated at the water-monolayer film on the smectite surface. Neutral organic molecules in the interlayer influences hydration spheres of the cations and their distance from the surface, while organic cations tend to substitute for inorganic ones.The third set of calculations aimed at testing mobility of organic model compounds within a wide-open smectite interlayer space (acting as a narrow pore model), under one-dimensional pressure. The results show significant differences in the pressure that allows expulsion of organic molecules in different systems and different ions from a narrow slit. The mobility of oil compounds depends mainly on differences in the type of molecules and the size of effective hydration sphere of the cations adsorbed on a mineral surface, which is clearly visible in the simulations.

Modification of Bentonite with Cationic and Nonionic Surfactants: Structural and Textural Features.

Surfactant-modified clay minerals are known for their good sorption properties of both organic and inorganic compounds from aqueous solutions. However, the current knowledge regarding the effect of both cationic and nonionic surfactants on the properties of bentonite is still insufficient. Bentonite, with montmorillonite as the base clay, was modified with hexadecethyltrimethylammonium bromide (a cationic surfactant) in the amount of 1.0 cation exchange capacity (CEC) of bentonite and varying concentrations of t-octylphenoxypolyethoxyethanol (Triton X-100, a nonionic surfactant). We aimed to improve the understanding of the effect of nonionic and cationic surfactants on clay minerals. The modified bentonites were characterized by X-ray diffraction (XRD), thermogravimetric analysis/differential thermal analysis (TG/DTA), Fourier transform infrared spectrometry (FTIR), field emission scanning electron microscopy (SEM) and specific surface area and pore volume (BET). According to our results, the presence of a cationic surfactant significantly increased the amount of the adsorbed nonionic surfactant. Moreover, an increase in the concentration of nonionic surfactants is also associated with an increase in the effectiveness of the modification process. Our results indicate that the amount of nonionic surfactant used has a significant effect on the properties of the obtained hybrid material. Modification of bentonite with a nonionic surfactant did not cause an expansion of the interlayer space of smectite, regardless of the presence of a cationic surfactant. The modification process was found to significantly decrease the specific surface area of bentonite. Improvement of hydrophobic properties and thermal stability was also observed.

Hydrothermal experiments reveal the influence of organic matter on smectite illitization

Smectite illitization is an important diagenetic phenomenon of mudstones, but only rarely has the influence of organic matter (OM) on this process been examined. In the present study, hydrothermal experiments were conducted with smectite (M1, total organic carbon (TOC) 1%). X-ray diffraction (XRD), infrared, X-ray fluorescence (XRF), and organic carbon analyses were employed to characterize the mineralogy and OM of the samples and the effect of OM on smectite illitization. The XRD patterns showed changes in clay mineral parameters with increased temperature. These changes varied in both M1 and M2 and indicated a difference in the degree of smectite illitization. Moreover, the OM in M2 was mainly adsorbed in smectite interlayers, the OM was largely desorbed/decomposed at temperatures above 350°C, and the OM was the main reason for differences in the degree of smectite illitization between M1 and M2. Bulk mineral composition, elemental content, and infrared absorption band intensities were changed with increased temperature (especially above 350°C). This indicated the formation of new minerals (e.g., ankerite). Overall, OM entered the interlayer space of smectite in M2 and delayed the exchange of K+ by interlayer cations, and thus, suppressed the transformation of smectite to illite and resulted in differences in smectite illitization of M1 and M2. In particular, the formation of CO2 after the decomposition of OM at temperatures above 300°C led to the formation of ankerite in M2. This demonstrated the effect of organic-inorganic interactions on smectite illitization and mineral formation. The disparities in smectite illitization between M1 andM2, therefore, were linked to differences in the mineral formation mechanisms of a water-rock system (M1) and a water-rock-OM system (M2) in natural environments. The insights obtained in the present study should be of high importance in understanding organic-mineral interactions, hydrocarbon generation, and the carbon cycle.

Structural characterization of chitosan-smectite nanocomposite and its application in the development of a novel potentiometric monohydrogen phosphate-selective sensor

Chitosan-smectite biocomposite was prepared by intercalation of protonated chitosan molecules into the interlayer space of smectite in monolayer arrangement through cation exchange mechanism and the obtained biocomposite was successfully used as an electroactive component in the structure of a PVC membrane potentiometric sensor for the direct and highly selective determination of monohydrogen phosphate ions. The comparative elemental, structural, thermal and morphological analysis of starting-smectite, neat chitosan and chitosan-smectite were investigated by utilizing EDX, XRD, ATR-FTIR, TG/DTG/DTA, SEM and surface area measurement techniques. The optimum membrane composition, detection limit, response time, pH working range and repeatability of the proposed electrode were determined.

Tunable High-Pressure Field Operating on a Cationic Biphenyl Derivative Intercalated in Clay Minerals

We propose a methodology for applying a pseudo uniaxial pressure to an organic molecule under ordinary temperature and pressure, namely by intercalation into smectites. The pseudo pressure on a biphenyl derivative (BP) was estimated from the averaged dihedral angle around the central bond of BP. In a high hydrostatic pressure field, biphenyl takes a planar conformation. In the interlayer space of synthetic saponite (SSA), the averaged dihedral angle of BP at a loading level of 27% versus the cation exchange capacity was ~26.3°, which indicates that the pseudo pressure applied to BP in the SSA interlayer space corresponds to 0.99 GPa. The high pseudo-pressure field in the interlayer space of SSA was also confirmed by absorption measurements. The dihedral angle around the central bond of the biphenyl moiety decreased to enhance the planarity of the molecule, mainly in response to the electrostatic force that operates between the negatively charged SSA layer and the interlayer cation. The pseudo pressure operating on BP in the smectite interlayer space could be controlled by varying the smectite layer charge density and/or the BP loading level. By using this methodology, controllable pseudo high-pressure properties of organic molecules can be obtained at ordinary temperatures and pressures.

Hydrothermal synthesis of zinc selenide in smectites

Nanohybrids of zinc selenide and smectites (a natural montmorillonite and a synthetic saponite) were prepared by a hydrothermal reaction of zinc chloride and sodium selenosulfite in the presence of smectites. The products were characterized by powder X-ray diffraction, scanning and transmission electron microscopies, thermogravimetric analysis, as well as, UV–visible and photoluminescence spectroscopies. The round-shaped zinc selenide nanoparticles with the average diameter of 1–4nm formed in the interlayer space of smectites, which gave the absorption onsets at 379–456nm for montmorillonite system and at 475nm for saponite system. Additional absorption onsets were observed at around 478–665nm for montmorillonite system and at 609–682nm for saponite system, suggesting the larger-sized particles formed at the external surfaces. The photoluminescence observed in the wavelength range of 357–360nm was interpreted to the formation of zinc selenide nanoparticles in smectites. The increase of the photoluminescence intensities of all the products (from 35 for bulk ZnSe to 126–294 for ZnSe(n)-smectites) was thought to be caused by the interactions with smectites and/or size and shape of ZnSe formed in the hybrids.

Dissolution of beidellite in acidic solutions: Ion exchange reactions and effect of crystal chemistry on smectite reactivity

The dissolution rate of beidellite, a dioctahedral smectite with tetrahedral charge that is a common swelling clay mineral in surface and subsurface natural environments, was studied in acidic solutions at 25°C under far from equilibrium conditions. A <0.3μm size fraction of SBId1 beidellite ((Si7.148Al0.852)(Al3.624Mg0.18Fe(III)0.224)O20(OH)4M+0.948) purchased from the Clay Mineral Society was used as the starting material, and experiments were performed in stirred flow-through reactors using HCl solutions with pH values ranging from 1 to 3. Several hydrodynamic conditions were tested using different flow rates with stirred and non-stirred particles. The aqueous Al/Si ratio measured at the outlet of the reactor was followed as a function of time and compared to solid stoichiometry values to assess the mechanisms occurring at the solid/solution interface. The reversible adsorption of Al3+ in the smectite interlayer space was evidenced for pH>1.1, and the presence of an amorphous Si-enriched layer can be reasonably assumed in some cases from the interpretation of the aqueous concentrations and the characterization of the solid phase (X-ray diffraction and FTIR spectroscopy). Beidellite dissolution rates normalized to the sample mass (molg−1s−1) were obtained from Si and Al concentrations under steady state dissolution conditions. Calculated rates were compared with those previously reported for montmorillonite in several publications. The beidellite dissolution rates are, on average, ten times lower than those of montmorillonite. This implies that the smectite crystal chemistry (i.e., amount of Al3+ versus Mg2+ or Fe3+ substitution in the structure) has a strong effect on its stability and should be considered in reactive transport models in which the dissolution properties of smectites are taken into account.

Influence of organic matter on smectite illitization: A comparison between red and dark mudstones from the Dongying Depression, China

Interactions between organic matter (OM) and clay minerals have received considerable attention in previous studies. The influence of OM on smectite illitization has been analyzed primarily in simulation experiments rather than in diagenetic studies. The present study explores the influence of OM on smectite illitization during diagenesis. Thirty red and dark mudstone samples from the Dongying Depression were analyzed. X-ray diffraction (XRD) analyses revealed that the illite percentages in mixed-layer illite-smectite (I-S) of both types of samples were dispersive above 3100 m and more convergent below this depth. The stacking mode of I-S in dark mudstones above 3100 m remained primarily at R0–R0.5 ordering with the average number of layers (Nave) dispersively distributed between 2 and 4.5. In red mudstones, the I-S changed from the R0 to R0.5 mode with the Nave increasing from 2 to 5. Over this range, the smectite illitization in dark mudstones was slower than that in red mudstones. Below 3100 m, the I-S stacking mode of dark mudstones changed from R0.5 to R3 ordering with the Nave increasing sharply from 4 to 8. In red mudstones, the I-S displayed R1.5 and R3 ordering with the Nave varying between 4.5 and 6.5. Over this range, the smectite illitization in dark mudstones accelerated rapidly, whereas the process in red mudstones was retarded. Additionally, the red mudstone samples contained little OM, whereas the dark mudstone samples contained abundant total organic carbon (0.17–4.43%). Thermo-XRD, near-infrared (NIR) as well as mid-infrared (MIR) spectroscopy analyses suggested that the OM in dark mudstones exhibited a significant transition at 3100 m, coincident with the illitization change. Above 3100 m, the smectite illitization in dark mudstones was delayed due to the OM pillar effect in the interlayer spaces of smectite. Below 3100 m, the interlayer OM became varied and desorbed, discharging organic acid. This led to the dissolution of smectite structural layers. Consequently, illitization in the dark mudstone was accelerated. This study revealed that the existence and occurrence of OM could influence the smectite illitization in diagenesis. Further study on the interactions between OM and clay minerals is needed to facilitate our understanding on the mechanism of smectite illitization as well as its geological applications.

The effects of pH, pepsin, exchange cation, and vitamins on aflatoxin adsorption on smectite in simulated gastric fluids

Aflatoxins are toxic secondary fungal metabolites that are present in a variety of crops. Adding bentonites to aflatoxin contaminated feed could reduce the toxicity to animals, yet a complete toxicity protection has not been achieved. The aflatoxin (AfB1) adsorption by bentonite in the gastrointestinal tract could be hindered by the competition of proteins and other nutrients. The objectives of this study were to evaluate 1) the effect of simulated gastric fluid protein (pepsin) and pH on aflatoxin adsorption by smectite, 2) the influence of the exchangeable cation of smectite on the aflatoxin adsorption in simulated gastric conditions, 3) the competition of vitamins with aflatoxin molecules for adsorption sites on the smectite, and 4) the aflatoxin adsorption in the presence of vitamin B1 in the simulated fluid.Aflatoxin adsorption isotherms were performed in water and simulated gastric fluids for smectites saturated with Na, Ca and Ba. The intercalation of pepsin in the smectite was confirmed with XRD and FTIR. The vitamin (B1, D and E) interaction was quantified with adsorption isotherms, too. Aflatoxin adsorption on smectite was reduced in the simulated gastric solution, due to the intercalation of pepsin onto the smectite. The exchangeable cation showed low or negligible effect on the aflatoxin adsorption in the simulated GF. Vitamin B1 was adsorbed by the clay.Proteins and hydrophilic vitamins competed with aflatoxin molecules for adsorption sites on smectite. In the interlayer space of smectite, large molecules as pepsin could block the hydrophobic sites required for aflatoxins. Yet, vitamin B1 could compete with proteins and enhance the adsorption of aflatoxin by yielding the hydrophobic domains on smectite surface.

Preparation and characterization of azobenzene-smectite photoactive mineral nanomaterials

Smectites are 2:1 layered minerals built of one octahedral sheet located between two tetrahedral sheets. The layer charge, derived from the isomorphic substitutions in the mineral structure, is compensated by the interlayer cations. The capability to exchange the interlayer cations is an important property of smectites as it enables to design and produce new nanomaterials based on natural minerals through their organic modification. Such hybrid materials are highly desirable in industry and environmental protection due to their specific properties that may be controlled in nanoscale. Preparation of photoactive materials through intercalation of layered minerals, including mainly synthetic micas, with azobenzene and other azo-compounds was proposed previously (Fujita et al., 2003; Ogawa et al., 2003 ; Heinz et al., 2008) . Azobenzene molecules show a change in their shape and dimensions upon the UV irradiation, which may affect the structure of host mineral. The photoactivate materials may find application in nanotechnology as molecular nanoswitches and nanosensors controlled by UV radiation. The objective of the study was to prepare azobenzene-smectite intercalation compounds. The obtained materials were subjected to structural and chemical characterization, which is crucial for further advancement of their photoresponsive properties. Na-montmorillonite (SWy), Ca-montmorillonite (STx), beidellite (BId) and synthetic laponite (SynL) were used for the experiments. The modification procedure involved at first the intercalation of smectites with hexadecyltrimethylammonium bromide (abbreviated C16) and after that the insertion of azobenzene into the interlayer space. The reaction with C16, in amount equal to 1.0 CEC of the smectite, was performed in an aqueous suspension (20g/L) for 2 h in 60°C. The obtained organo-smectites were prepared as thin films on glass plates and reacted with azobenzene in a teflon vessel at ~100°C for 24 h.In such conditions the azobenzene vaporizes and penetrates the interlayer space of the organo-mineral. The azobenzene/smectite weight ratio was equal to 0.2. The chemical and structural analysis of all obtained samples was carried out with use of X-ray diffraction (XRD), infrared spectroscopy (FTIR) and CHN elemental analysis. The increased amount of nitrogen and carbon in modified samples confirmed the occurrence of intercalation process of both the ammonium salt and the azobenzene. Moreover, new bands appeared in the infrared spectra of the C16-smectites at ~2924 cm -1 and ~2851 cm -1 due to the C-H stretching vibrations in the C16 molecules. The spectra of azobenzene intercalation compounds showed additionally a series of bands corresponding to the vibrations characteristic for the azobenzene molecule at: ~3061 cm -1 , ~1581 cm -1 , ~1455 cm -1 , and ~1302 cm -1 . . The basal spacing of tested minerals increased after the C16 intercalation, as confirmed by the XRD analysis. The increase was equal to 6.1 A, 3.3 A, 4.1 A and 3.5 A for SWy, STx, BId and SynL samples, respectively. This suggests a nearly horizontal arrangement of C16 molecules and formation of a monolayer in the interlayer space of smectite. Introduction of azobenzene lead to a further increase of d 001 value. The increase is visibly different for all the samples and is equal to 7.0 A, 15.0 A, 21.7 A and 23.5 A for SWy, STx, BId and SynL samples, respectively . The arrangement of organic molecules in the interlayer space is influenced by a number of factors including: the type of the mineral, the layer charge and its location in the layer, or the amount and arrangement of the cationic surfactant . A correlation between the azobenzene location in the interlayer space and the photoresponse behavior of tested materials will be the subject of further studies.

The effect of cetyltrimethylammonium ion and type of smectites on the luminescence efficiency of bis(8-hydroxyquinoline)zinc(II) complex

A luminescence metal complex, bis(8-hydroxyquinoline)zinc(II) (Znq2), was incorporated into the interlayer space of smectites (a natural montmorillonite and a synthetic saponite) by two different ways; colloidal processes via the in situ formation of bis(8-hydroxyquinoline)zinc(II) in cetyltrimethylammonium-smectites (CTA-smectites) and the adsorption of cetyltrimethylammonium coated bis(8-hydroxyquinoline)zinc(II) (Znq2CTA) into hydrophilic smectites. The UV–Vis spectra confirmed the formation and the incorporation of bis(8-hydroxyquinoline)zinc(II) in the interlayer space of smectites. The photoluminescence bands of Znq2CTA@montmorillonite and Znq2@CTA-montmorillonite (498nm) were blue shifted in comparison with the weak emission bands of Znq2CTA@saponite and Znq2@CTA-saponite (510nm), indicating the formation of different nanostructures and/or packing of bis(8-hydroxyquinoline)zinc(II) in the two types of smectites. The state of the intercalated cetyltrimethylammonium ions also played a key role to the luminescence intensities of the products due to the concentration quenching and self-absorption.

Water Orientation in Smectites Using NMR Nutation Experiments

We observed the arrangement of water molecules when confined in the interlayer space of smectites using low field nutation experiments. Despite the presence of paramagnetic impurities that prevent such observation at high field, we can determine the amount of water in strong interaction with the clay surface, i.e., water molecules which are partially oriented within each platelet. The experiments do not require the orientation of the clay platelets relative to the magnetic field. We present the NMR theory, the signal processing, and the results on a series of 4 homoionic smectites (Na, Ca, Mg, and K) at different relative humidities in order to vary the water content and the basal spacing. In these systems, we found that between 0.5 and 2.5 water molecules per ion are oriented.

Direct evidence for organic carbon preservation as clay-organic nanocomposites in a Devonian black shale; from deposition to diagenesis

The burial of marine sourced organic carbon (OC) in continental margin sediments is most commonly linked to oceanographic regulation of bottom-water oxygenation (anoxia) and/or biological productivity. Here we show an additional influence in the Devonian Woodford Shale, in which OC occurs as nanometer intercalations with specific phyllosilicate minerals (mixed-layer illite/smectite) that we term organo-mineral nanocomposites. High resolution transmission electron microscopic (HRTEM) images provide direct evidence of this nano-scale relationship. While discrete micron-scale organic particles, such as Tasmanites algal cysts, are present in some lamina, a strong relation between total organic carbon (TOC) and mineral surface area (MSA) over a range of 15% TOC indicate that the dominant association of organic carbon is with mineral surfaces and not as discrete pelagic grains, consistent with HRTEM images of nanocomposites. Where periods of oxygenation are indicated by bioturbation, this relationship is modified by a shift to lower OC loading on mineral surfaces and reduced MSA variability likely resulting from biological mixing and homogenization of the sediment, oxidative burn down of OC and/or stripping of OC from minerals in animal guts. The TOC–MSA relationship extends across a range of burial depths and thermal maturities into the oil window and persists through partial illitization. Where illitization occurs, the loss of mineral surface area associated with the collapse of smectite interlayer space results in a systematic increase in TOC:MSA and reorganization of organic carbon and clays into nano-scale aggregates. While the Woodford Shale is representative of black shale deposits commonly thought to record heightened marine productivity and/or anoxia, our results point to the importance of high surface area clay minerals for OC enrichment. Given that the vast majority of these clay minerals are formed in soils before being transported to continental margin settings, their mineralogy and attendant preservative potential is primarily a function of continental climate and provenance making these deposits a sensitive recorder of land as well as oceanographic change.

Adsorption of glycine on montmorillonite in aqueous solutions

Glycine was adsorbed on the surface of montmorillonite from aqueous solutions of variable glycine concentrations (0.001–0.3molL−1) and pHs (2–12) at room temperature. The reaction products were characterized using X-ray diffraction and attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy. The results indicate that adsorption is highly pH dependent, increasing at acidic pHs. Glycine adsorption is dominated by complexation of the carboxylate group of zwitterionic glycine onto the edge surface at low concentrations of glycine. When the edge surface is saturated, the adsorption occurs by cation exchange in the interlayer space. ATR-FTIR results point to an adsorption by hydrogen bonding between the NH3+ group and the basal oxygen of the interlayer surface. The dependence of glycine adsorption with its aqueous concentration fits for a Freundlich equation. The measure of the desorbed interlayer cations shows that the 68% of the K+ was exchanged with glycine. The K+–glycine exchange reaction produces a decrease of the smectite interlayer space from 14.5 to 12Å and an arrangement of the smectite layers. Intercalated glycine is present as both glycinium and zwitterionic forms. Since only glycinium contribute to structural charge balance, total adsorbed glycine can exceed K+ released. These findings are of relevance for the evaluation of distribution and reactions of free amino acids in natural environments.

Morphology, Structure, Thermal Stability, XR-Diffraction, and Infrared Study of Hexadecyltrimethylammonium Bromide–Modified Smectite

We characterized the interlayer structure and morphology of modified natural clays. Organoclay-based materials are increasingly used for multiple applications. We modified a purified Na-bentonite using cation exchange with hexadecyltrimethyl ammonium bromide (HDTMA) and characterized it using; UV spectroscopy, X-ray diffraction, photoacoustic FTIR spectroscopy (PA-FTIR), thermogravimetric analysis (TGA) techniques, laser scattering distribution (LSD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The adsorption of HDTMA on interlayer sites of Na-smectite fraction is nearly total until an adsorption equivalent to 1.85 times the cation exchange capacity (CEC) of the clay. The formation of the HDTMA-smectite changes the properties of the clay from hydrophilic to hydrophobic. The XRD patterns show an increase in the basal spacings. TGA characterization and analysis were shown to be useful to estimate the amount of surfactant within the organoclay. LSD analyses have shown a decrease of the effective particle diameter with increasing sonication times. AFM images showed that these Na-smectite surfaces appeared foliated with irregular aggregate structures at high HDTMA loading. The present study shows that not only the basal spacing but the morphology and the particle size of the organoclay strongly depend on the packing density of surfactant within the smectite interlayer space.

Characterization of natural- and organobentonite by XRD, SEM, FT-IR and thermal analysis techniques and its adsorption behaviour in aqueous solutions

AbstractIn this study, natural bentonite was modified with hexadecyltrimethylammonium (HDTMA) bromide to obtain organobentonite (HDTMA-bentonite). Bentonite and HDTMA-bentonite were then characterized using XRD, XRF, SEM, FT-IR, thermogravimetric (TG) analysis, elemental analysis and Brunauer-Emmett-Teller (BET) surface area techniques. The HDTMA+ cation was found to be located on the surface and enters the interlayer spaces of smectite according to the XRD and SEM results. FT-IR spectra indicated the existence of HDTMA functional groups on the bentonite surface. The BET surface area significantly decreased after the modification due to the coverage of the pores of natural bentonite. After the characterization, the adsorption of a textile dye, Reactive Blue 19 (RB19), onto bentonite and HDTMA-bentonite was investigated. The maximum adsorption capacity of HDTMA-bentonite for RB19 was 502 mg g-1 at 20°C. The adsorption process followed a pseudo-second-order kinetic model and it was exothermic and physical in nature.