Smectite Interlayers Research Articles

Equimolar cation exchange of polyacrylamide in smectite

Smectite-polymer composites from cationic polyacrylamide (PAMS,τ40Cl) were prepared to investigate the adsorption behavior of the smectite after the intercalation procedure. PAMS,τ40Cl solutions with two different concentrations (γ = 5.18 g/L corresponds to 4.3 mmol/L and γ = 3 g/L corresponds to 4.3 mmol/L) were used to manufacture smectite-PAM+S,τ40 composites. The total amount of PAM+S,τ40 intercalated into the interlayer of the smectite was between 4.5 and 10%. This corresponds to coverage between 4 and 11 cmol(+)/kg, based on the cation exchange capacity (CEC) of the smectite. The smectite in the smectite-PAM+S,τ40 composites still possesses a CEC. The CEC decreased with increasing PAM+S,τ40 content. The CEC decrease was higher than the effective coverage. The amount of Na+ in the interlayer decreased compared to the initial amount with increasing PAM+S,τ40 content. PAM+S,τ40 prefers the interlayer with Na+. Smectite particles in the used raw bentonite (MX-80) are large enough for a planar covering of the basal surfaces by PAMS,τ40Cl. Furthermore, the distances between the charges at the basal surfaces of the smectite and in the oligomer are also large enough for planar covering. Evaluation of the mass spectrometer (MS) curve of m/z = 35 (Cl2) showed that PAM+S,τ40 does not saturate all charges of the smectite per unit cell. Some charges of PAM+S,τ40 are still saturated by Cl−. The exchange of PAM+S,τ40 for Na + in the interlayer of smectite takes place equimolar.

Thermodynamic data of adsorption reveal the entry of CH4 and CO2 in a smectite clay interlayer.

The ability of smectite clays to incorporate gases in their interlayers is shown to be conditioned by interlayer spacing, depending, in turn, on phyllosilicate layer composition and effective size of the charge-balancing cations. As illustrated by earlier in situ X-ray diffraction and spectroscopic characterization of the gas/clay interface, most smectites with small-size charge-balancing cations, such as Na+ or Ca2+, accommodate CO2 and CH4 in their interlayers only in a partially hydrated state resulting in the opening of the basal spacing, above a certain critical value. In the present study CH4 and CO2 adsorption isotherms were measured for Na- and Mg-exchanged montmorillonite up to 9 MPa using a manometric technique. The process of dehydration of these clays was thoroughly characterized by thermogravimetric analysis and powder X-ray diffraction. A dramatic decrease in specific surface area and methane and carbon dioxide adsorption capacities for fully dehydrated samples in comparison to partially dehydrated ones is assigned to the shrinkage of interlayer spacing resulting in its inaccessibility for the entry of CH4 and CO2 molecules. This observation is direct evidence of CH4 and CO2 adsorption capacity variation depending on the opening of smectite clay interlayer spacing.

Semiarid climate and hyposaline lake on early Mars inferred from reconstructed water chemistry at Gale

Salinity, pH, and redox states are fundamental properties that characterize natural waters. These properties of surface waters on early Mars reflect palaeoenvironments, and thus provide clues on the palaeoclimate and habitability. Here we constrain these properties of pore water within lacustrine sediments of Gale Crater, Mars, using smectite interlayer compositions. Regardless of formation conditions of smectite, the pore water that last interacted with the sediments was of Na-Cl type with mild salinity (~0.1–0.5 mol/kg) and circumneutral pH. To interpret this, multiple scenarios for post-depositional alterations are considered. The estimated Na-Cl concentrations would reflect hyposaline, early lakes developed in 104–106-year-long semiarid climates. Assuming that post-depositional sulfate-rich fluids interacted with the sediments, the redox disequilibria in secondary minerals suggest infiltration of oxidizing fluids into reducing sediments. Assuming no interactions, the redox disequilibria could have been generated by interactions of upwelling groundwater with oxidized sediments in early post-depositional stages.

Crystal structure model development for soil clay minerals – I. Hydroxy-interlayered smectite (HIS) synthesized from bentonite. A multi-analytical study

During the acidic weathering of soils, aluminum (Al) is dissolved from primary silicates such as feldspars or chlorites and intercalated in layer silicates. Part of this Al polymerizes in the interlayer of former smectites or vermiculites and the resulting phases are called hydroxy-interlayered minerals. These phases are known for a long time but are still insufficiently understood in terms of chemical composition and crystallographical structure. In the present study a sample set consisting of a continuous series of hydroxy-interlayered smectite samples with different degrees of hydroxy-interlayering ranging from 0 to 96% mol/mol smectite/HIS was prepared from a bentonite sample by adding different amounts of a 0.1 mol/L AlCl3 solution and different reaction times. The products were investigated by a multi-analytical approach using X-ray diffraction, Infrared spectroscopy, X-ray Fluorescence spectrometry, Fe2+:Fetotal determination, Nuclear Magnetic Resonance spectroscopy, Simultaneous Thermal Analysis coupled with mass spectrometry and Cation Exchange Capacity to provide an in-depth characterization. X-ray diffraction indicated that the turbostratic disorder typical for smectite did not change during hydroxy-interlayering. Nuclear Magnetic Resonance spectroscopy proved the exclusive six-fold coordination of interlayer Al and based on chemical calculations the average size and charge of the interlayer structures were characterized. Hydroxy-interlayers evolved in-situ in the smectite interlayers by polymerization. These interlayer “polymers” were small oligomers, the average size of which increased from monomers to pentamers with increasing degree of hydroxy-interlayering while the average net charge of each oligomer decreased. An average structural formula of each interstratified smectite-hydroxy-interlayered smectite was calculated from X-ray Fluorescence data including Fe2+:Fetotal ratios. If all exchangeable cations are attributed to smectite layers and all hydroxy-interlayers are attributed to hydroxy-interlayered smectite layers, the degree of hydroxy-interlayering ranged from 0 to 96% mol/mol smectite/HIS. The analysis provides an improved structural model of hydroxy-interlayered smectite suitable for Rietveld refinement which can be used to quantify the amounts of hydroxy-interlayered smectite in natural samples.

Temperature dependent structure and dynamics in smectite interlayers: 23Na MAS NMR spectroscopy of Na-hectorite.

23Na MAS NMR spectroscopy of the smectite mineral hectorite acquired at temperatures from −120 °C to 40 °C in combination with the results from computational molecular dynamics (MD) simulations show the presence of complex dynamical processes in the interlayer galleries that depend significantly on their hydration state. The results indicate that site exchange occurs within individual interlayers that contain coexisting 1 and 2 water layer hydrates in different places. We suggest that the observed dynamical averaging may be due to motion of water volumes comparable to the dripplons recently proposed to occur in hydrated graphene interlayers (Yoshida et al. Nat. Commun., 2018, 9, 1496). Such motion would cause rippling of the T-O-T structure of the clay layers at frequencies greater than ∼25 kHz. For samples exposed to 0% relative humidity (R.H.), the 23Na spectra show the presence of two Na+ sites (probably 6 and 9 coordinated by basal oxygen atoms) that do not undergo dynamical averaging at any temperature from −120 °C to 40 °C. For samples exposed to R.H.s from 29% to 100% the spectra show the presence of three hydrated Na+ sites that undergo dynamical averaging beginning at −60 °C. These sites have different numbers of H2O molecules coordinating the Na+, and diffusion calculations indicate that they probably occur within the same individual interlayer. The average hydration state of Na+ increases with increasing R.H. and water content of the clay.

Time-dependent unsaturated behaviour of geosynthetic clay liners

Three different chilled-mirror hygrometer test procedures were developed to investigate the time-dependent unsaturated behaviour of powdered and granular bentonite based needle-punched geosynthetic clay liners (GCLs) on both the wetting and drying paths of the water retention curve (WRC). The GCL structure and bentonite forms governed the effect of measurement time and duration as well as the time-dependent suction changes of the bentonite component at a constant gravimetric water content. A conceptual model is proposed to explain the observed time-dependent unsaturated behaviour of the GCLs. The model suggests that the cross-over points on WRCs correspond to the point where bentonite crystallite separation is maximized within the crystalline swelling regime of smectite, forming a four-layer hydrate state where smectite interlayer spaces are filled with water. At gravimetric water contents below this point, the interlayer space dominated the suction, while at higher water contents, mesopores and macropores played increasingly important roles in determining the suction. The results reported herein provide further proof that the unsaturated behaviour of GCLs is largely controlled by the bentonite component.

A contrastive study of effects of different organic matter on the smectite illitization in hydrothermal experiments

Although influence of organic matter (OM) on smectite illitization has received considerable attention in previous studies, the effect of different OM types on smectite illitization mechanism has rarely been examined. In the present study, hydrothermal experiments were conducted with N,N-dimethylhexadecylamine (16DMA)-smectite (M2) and lysine-smectite (M3) complexes to explore the effect of OM types on smectite illitization mechanisms. X-ray diffraction (XRD) analysis showed that mineral contents, illite percentage in mixed-layer illite-smectite (I% in ISm), the average number of layers (Nave), and stacking mode of ISm changed weakly at <300 °C while changed greatly at >300 °C. The changes varied obviously between M2 and M3 at >300 °C, indicating characteristics of solid-state transformation illitization mechanism in M2 and dissolution crystallization mechanism in M3. Moreover, the mid-infrared and thermo-XRD analyses indicated that the OM was mainly adsorbed in smectite interlayers at <300 °C, which delayed the exchange of K+ by interlayer cations and thus suppressed the smectite illitization. Above 300 °C, the OM was largely desorbed and the resulting changes of solution properties led to the acceleration of illitization and difference in illitization mechanisms in M2 and M3. The bulk mineralogy, element, and infrared analyses showed that illitization was accompanied by formation of new minerals and more minerals were formed in M2 than M3. The new minerals were further increased above 300 °C, especially the ankerite in M2. The binding mechanisms and strength varied in M2 and M3 because of differences in OM types, resulting in differences in bulk mineralogy evolution. This demonstrated the effect of organic-inorganic interactions on smectite illitization and mineral formation. The disparities in smectite illitization between M2 and M3, therefore, were linked to differences in mineral evolution of water-rock-OM systems with different OM types in natural environments. The insights obtained in the present study should be of high importance in understanding organic-inorganic interactions, hydrocarbon generation, and the carbon cycle.

An experimental study on smectites as nitrogen conveyors in subduction zones

We performed high pressure and high temperature (HPHT) experiments on NH4-doped montmorillonite (~2 wt% of NH4) under pressures of 2.5, 4.0, and 7.7 GPa and temperatures from 200 to 700 °C. Each experiment was analyzed with XRD, FTIR, CHN elemental analysis, and SEM in order to determine the NH4-Smectite phase changes and their morphology, and the presence of ammonium in the runs. Our results show that smectite can easily transport nitrogen, speciated as ammonium (NH4+), incorporated into the smectite interlayer in mildly reducing environments to deeper levels in the Earth through cold thermal regime subduction zones. NH4-Smectite transforms into NH4-enriched micaceous phase (tobelite) through a NH4+-enriched interlayered I/S phase in relatively low pressures and temperatures (around 2.5 GPa and 500 °C). Tobelite is stable until more extreme conditions (7.7 GPa and 700 °C), together with lesser amounts of buddingtonite (an ammonium-bearing feldspar) kyanite, and garnet. Our experiments also show the effect of nitrogen in the feldspar stability, as potassic and sodic feldspar are stables until ~5 GPa, while buddingtonite, is stable at 7.7 GPa. Nitrogen can return to the surface once the stability of these nitrogen-enriched minerals is reached due to pressure or temperature increasing.

Development and characterization of clarithromycin-smectite hybrid for burst release at high pH condition

In this study, we developed and characterized a clarithromycin (CLR)-intercalated smectite hybrid and demonstrate that it holds great potential as an effective drug-carrier for local delivery of CLR. The intercalation of CLR into a smectite interlayer was examined at 0.4–4.0 mg ml−1 of CLR solution at pH 5. The developed CLR-intercalated smectite hybrid was characterized using x-ray diffraction (XRD), UV–vis spectroscopy, energy dispersive x-ray spectroscopy (EDS), thermogravimetric-differential thermal analysis (TG-DTA) and Fourier transform infrared spectroscopy (FT-IR). Intercalation of CLR was confirmed by an increase in the d-spacing in the XRD pattern and the ether absorbance band in the FT-IR spectrum for the CLR hybrid. An in vitro release study demonstrates that most of the CLR was released from the hybrid in both low pH condition (pH 1.2) and high pH condition (pH 7.4) fluids within 60 min. Compared with the conventional tablet form, approximately 4-times more CLR was released within 1 h at high pH conditions, indicating suitable local therapeutic performance. Therefore, Helicobacter pylori, which is located only in the gastric mucosal layer could be a good target organism for this hybrid. In conclusion, smectite could be a suitable carrier for local delivery of intercalated drug, and CLR intercalated smectite could be a new option for local therapy of gastrointestinal conditions.

Salinity Reversal and Water Freshening in the Eagle Ford Shale, Texas, USA

Effective, considerate shale play water management supports operations and protects the environment. A parameter often overlooked is total dissolved solids (TDS) of produced water from the formation. Knowledge of TDS is important to meet these dual goals. Subsurface TDS typically increases with depth. However, produced-water samples from the Eagle Ford Shale show a strong TDS decrease by a factor of ∼10 with increasing well depth (∼200 000 ppm at ∼2.5 km to 18 000 ppm at ∼3.6 km). Water stable isotopes strongly suggest that the low TDS is not due to dilution by meteoric water. Rather, we attribute the change to smectite-to-illite conversion, in which the smectite interlayer water is released into the pore space. Depth, temperature, and other related indicators (source for K, excess silica) support such a mechanism. In addition, water-isotope patterns and 87Sr/86Sr ratios suggest a conversion operating with limited contributions external to the shale. Order-of-magnitude calculations show that the 8% of mix...

Geochemical conditions for the formation of Mg silicates phases in bentonite and implications for radioactive waste disposal

The present study evaluates the formation of magnesium silicates phases as a result of the alkaline alteration of FEBEX bentonite in long-term experiments. The results are relevant in the context of radioactive waste disposal since the bentonite barrier will partly change its original mineralogy and condition its long-term geochemical behavior. Bentonite samples from an in situ experiment of interaction with a CEM-II-type concrete performed for 13 years in a rock gallery and a laboratory experiment of interaction with a CEM-I-type concrete performed for 10 years provide some experimental evidences on the mineralogical alteration. Results required multiple analytical techniques to resolve the nature of the Mg silicates. X-ray diffraction, thermogravimetric analyses, scanning electron microscopy, infrared spectroscopy and 27Al and 29Si nuclear magnetic resonance have been used. The mineralogical alteration is complex since several Mg silicates may coexist in the same region not only with themselves but also with carbonates and calcium (aluminium) silicate hydrates. Brucite intercalation in the interlayer of smectite, previously reported as a chlorite-like phase in a former study, is observed. In addition, a serpentine-type mineral phase was better observed in the in situ samples, at least by XRD, and a 2:1 trioctahedral phyllosilicates was better observed in the laboratory samples. Formation of Mg silicates in the bentonite barrier may buffer the Ca alkaline front originated in concrete and may decrease the porosity at the concrete-bentonite interface.

Application of polyether amine, poly alcohol or KCl to maintain the stability of shales containing Na-smectite and Ca-smectite

ABSTRACTThe stability of a shale containing smectite with different exchangeable cations (Na+, Ca2+) was improved using optimum solutions containing polyether amine (PA), poly-alcohol (PO) or KCl. Two types of shale samples with Na+ and Ca2+ as the main exchangeable cations, respectively, were used and the optimized solutions were determined using X-ray diffraction (XRD), an adsorption test, an oedometer swelling test, and an immersion test. The use of KCl prevented intercalation of PA or PO and maintained the stability of the Na-smectite-bearing shale. PA or PO adsorption reduced water adsorption sites on the clay layer, and K+ reduced hydration of exchangeable Na+, resulting in good shale stability in mixed solutions of KCl+PA, and KCl+PO. More stable shale was achieved in KCl+ PA mixed solution, whereas in the KCl+ PO solution the transport of water or solute molecules in the shale was reduced. In the shale containing mainly Ca-smectite, PA, PO and KCl maintained shale stability when applied separately or in common, as PA or PO cannot exchange Ca2+ in the smectite interlayer. As a result, PA or PO should be used together with KCl during drilling in shale formations containing Na-smectite, whereas in shales with Ca-smectite, PA, PO or KCl may be used separately.

Hydrothermal Experiments Reveal the Influence of Organic Matter on Smectite Illitization

AbstractSmectite 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) &lt;0.3%) and a smectite and N,N-dimethylhexadecylamine (16DMA) complex (M2, TOC &gt;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.

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.

Surfactant-intercalated smectite modified electrode: sensitive electrochemical detection of methyl orange dye

ABSTRACTThis work describes the use of organosmectite modified electrode to evaluate the electrochemical behaviour and to develop an electroanalytical procedure for the determination of methyl orange (MO) dye in natural water. Organosmectites were prepared by intercalation of hexadecyltrimethylammonium cations at various ratios into the interlayer of smectite. The synthesised organosmectites were characterised by various physicochemical techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. An amperometric sensor based on organosmectite as electrode modifier for MO sensing purposes was then evaluated by means of clay-film modified electrode using square wave voltammetry (SWV). The electrochemical procedure for MO analysis by stripping voltammetry involves two successive steps: accumulation of MO at open circuit conditions followed by a voltammetric detection in a same medium by the SWV technique. The peak current obtained (after 5 min preconcentration of 15 µmol L−1 MO solution) on a glassy carbon electrode coated by a thin film of the modified clay was more than 2.5 times higher than that exhibited by the same substrate covered by a film of the pristine clay. Under optimised conditions, a linear calibration curve for MO was obtained in the concentration range from 0.1 to 1.6 µmol L−1, leading to a detection limit of 4 × 10−8 mol L−1 (signal-to-noise ratio equal to 3). The interfering effect of various inorganic and organic ions likely to influence the stripping determination of the MO was also examined. To further validate application of this sensor, the proposed method was successfully used to the determination of MO in natural water with satisfactory results.

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.

A strontium isotope and trace element geochemical study of dolomite-bearing bentonite deposits in Bavaria (Germany)

AbstractThe Landshut bentonites that formed from Ca- and Mg-poor rhyolitic tuffs in a fluviatile-lacustrine depositional environment of the Miocene Upper Freshwater Molasse, southern Germany, contain abundant palustrine, pedogenic and groundwater carbonates. Geochemical analyses of dolomites, calcites and smectites from bentonites of various environments by X-ray diffraction, thermal ionization mass spectrometry, inductively coupled plasma-mass spectrometry, and handheld X-ray fluorescence yield new insights into the compositions of fluids and sources of imported components involved in carbonate formation and bentonitization, as well as the timing of bentonite formation. Evaporated, Sr-rich brackish surface water with a molar Mg/Ca ratio of 2–5, derived mostly from the weathering of detrital carbonates, was involved in dolomite and bentonite formation in palustrine and some pedogenic environments. However, Sr-poor groundwater with a molar Mg/Ca ratio of ∼ 1 and a stronger silicate weathering component caused bentonite and calcite formation in strictly pedogenic and groundwater settings. The 87Sr/86Sr and molar Mg/Ca in the smectite interlayers indicate later cation exchange with water having more radiogenic Sr sources and smaller molar Mg/Ca ratios. The Rb-Sr data indicate the common presence of detrital illitic phases in the &lt;0.2 μm fractions of the bentonites. Cogenetic palustrine dolomite and a single smectite residue sample which lacks this detrital illitic phase provide an age constraint for bentonitization at 14.7 ± 4.1 Ma identical to primary ash deposition. Thus a rapid onset of bentonitization of accumulated ash and dolomite formation in evaporation-driven wetland environments is indicated for the genesis of the Landshut bentonites.

Structural changes in smectite due to interaction with a biosurfactant-producing bacterium Pseudoxanthomonas kaohsiungensis

Clays including bentonite hold a great potential in improving the efficacy of organic contaminants degradation by bacteria. However, the mechanisms of interactions involving both biotic (microorganisms) and abiotic (clays) components during bioremediation are largely unknown. Here, we report the interaction of a biosurfactant producing bacterium, Pseudoxanthomonas kaohsiungensis, with bentonite clay. Using instrumental analyses including X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, inductively coupled plasma mass spectroscopy (ICP-MS), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) techniques we investigate the microstructural changes of smectite following introduction of the bacterium. The interaction resulted in a spherical clay-bacterial micro-agglomerate formation which deciphered an enhanced growth of the bacterium in a minimal medium supplemented with traces of olive oil. The bacterium brought about a significant dissolution of silicon (Si) preferentially from the tetrahedral silica edges of smectites. The deposition of bacterial biosurfactants and exopolysaccharides (EPS) slightly expanded the smectite interlayers and modified the clay's interaction with water molecules. This study has direct implication in the clay-mediated bioremediation of hydrophobic organic contaminants in the environment.

Structure and Dynamics of Water—Smectite Interfaces: Hydrogen Bonding and the Origin of the Sharp O-Dw/O—Hw Infrared Band From Molecular Simulations

AbstractExperimental studies have shown that a sharp, high-frequency IR band at ~3615 cm-1 (in H2O form) and at ~2685 cm-1 (in D2O form) is a common feature for all smectites, and its position correlates with layer charge. In order to explain the molecular origin of this band in terms of total layer charge, charge localization, as well as nature of interlayer cations influencing the position and intensity of this peak, a series of classical molecular dynamics (MD) simulations was performed for several smectite models. The smectite layers were described using a modified CLAYFF force field, where the intramolecular vibrations of H2O were described more accurately by the Toukan-Rahman potential. The power spectra of molecular vibrations of hydrogens were calculated for selected sub-sets of interlayer H2O to analyze quantitatively their contribution to the observed spectral features. The statistics of hydrogen bonds in the smectite interlayers were also analyzed to support the spectral calculations.The simulation results demonstrated clearly that only the H2O molecules in close proximity to the smectite surface are responsible for the sharp vibrational band observed. Other hypotheses for the possible origins of this band were considered carefully and eventually rejected. Two orientations of H2O molecules donating one or two H bonds to the basal oxygens of the smectite surface (monodentate and bidentate orientations, respectively) were observed. In both orientations, these H bonds are quite weak, pointing to a generally hydrophobic character of the smectite surface. Both orientations contributed to the high-frequency band, but the monodentate orientation provided the predominant contribution because surface H2O molecules in this orientation were much more abundant. In good agreement with experiment, only a small difference in the peak position was observed between smectites with different charge localization. The effect of the total layer charge, i.e. the red-shift for higher-charge smectites, was also confirmed. This shift arose from the decrease in the H-bonding distances of H2O in monodentate and bidentate orientation.

Characterization of a hybrid-smectite nanomaterial formed by immobilizing of N-pyridin-2-ylmethylsuccinamic acid onto (3-aminopropyl)triethoxysilane modified smectite and its potentiometric sensor application

A novel N-pyridin-2-ylmethylsuccinamic acid-functionalized smectite nanomaterial was synthesized by immobilizing of N-pyridin-2-ylmethylsuccinamic acid through chemical bonding onto (3-aminopropyl)triethoxysilane modified smectite. The structural, thermal, morphological and surface properties of raw, silane-grafted and the N-pyridin-2-ylmethylsuccinamic acid-functionalized smectites were investigated by various characterization techniques. The thermal analysis data showed the presence of peaks in the temperature range from 200 °C to 600 °C due to the presence of physically adsorbed silanes, intercalated silanes, surface grafted silanes and chemically grafted silane molecules between the smectite layers. The powder x-ray diffraction patterns clearly indicated that the aminopropyl molecules also intercalated into the smectite interlayers as bilayer arrangement whereas N-pyridin-2-ylmethylsuccinamic acid molecules were only attached to 3-aminopropyltriethoxysilane molecules on the external surface and edges of clay and they did not intercalate. Fourier transform infrared spectroscopy confirms N-pyridin-2-ylmethylsuccinamic acid molecules bonding through the amide bond between the amine group of aminopropyltriethoxysilane molecules and a carboxylic acid functional group of N-pyridin-2-ylmethylsuccinamic acid molecules. The guest molecules functionalized onto the smectite caused significant alterations in the textural and morphological parameters of the raw smectite. The anchoring of N-pyridin-2-ylmethylsuccinamic acid molecules led to positive electrophoretic mobility values when compared to starting materials. N-pyridin-2-ylmethylsuccinamic acid-functionalized smectite was employed as an electroactive ingredient in the structure of potentiometric PVC-membrane sensor. The sensor exhibited more selective potentiometric response towards chlorate ions compared to the other common anionic species.