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Aflatoxins can cause intoxication and poisoning in animals and humans. Among these molecules, aflatoxin B1 (AFB1) is the most dangerous because of its carcinogenic and mutagenic properties. To mitigate these effects, clay adsorbents are commonly included in the diet of animals to adsorb the carcinogens and prevent their absorption in the gastrointestinal tract. In this study, four clays, three smectites (C-1, C-2, and C-3), and one zeolite (C-4), were compared as adsorbents of AFB1 and trace inorganic nutrients using an in vitro gastrointestinal model for poultry. Characterization of the clays using Fourier transform infrared spectroscopy revealed characteristic bands of smectites in C-1, C-2, and C-3 (stretching vibrations of Si-O, Al-O-Si, and Si-O-Si). The C-4 presented bands related to the bending vibration of structural units (Si-O-Si and Al-O-Si). X-ray diffraction analysis showed that C-1 is a montmorillonite, C-2 is a beidellite, C-3 is a beidellite-Ca-montmorillonite, and C-4 is a clinoptilolite. The elemental compositions of the clays showed alumina, silica, iron, calcium, and sodium contents. The cation exchange capacity was higher in C-3 clay (60.2 cmol(+)/kg) in contrast with the other clays. The AFB1 adsorption of C-1 was the highest (98%; p ˂ 0.001), followed by C-2 (94%). However, all the clays also sequestered trace inorganic nutrients (Fe, Mn, Zn, and Se). Both smectites, montmorillonite and beidellite, were the most suitable for use as adsorbents of AFB1. [ABSTRACT FROM AUTHOR]

The understanding of the structural formula of smectite minerals is basic to predicting their physicochemical properties, which depend on the location of the cation substitutions within their 2:1 layer. This implies knowing the correct distribution and structural positions of the cations, which allows assigning the source of the layer charge of the tetrahedral or octahedral sheet, determining the total number of octahedral cations and, consequently, knowing the type of smectite. However, sometimes the structural formula obtained is not accurate. A key reason for the complexity of obtaining the correct structural formula is the presence of different exchangeable cations, especially Mg. Most smectites, to some extent, contain Mg2+ that can be on both octahedral and interlayer positions. This indeterminacy can lead to errors when constructing the structural formula. To estimate the correct position of the Mg2+ ions, that is their distribution over the octahedral and interlayer positions, it is necessary to substitute the interlayer Mg2+ and work with samples saturated with a known cation (homoionic samples). Seven smectites of the dioctahedral and trioctahedral types were homoionized with Ca2+, substituting the natural exchangeable cations. Several differences were found between the formulae obtained for the natural and Ca2+ homoionic samples. Both layer and interlayer charges increased, and the calculated numbers of octahedral cations in the homoionic samples were closer to four and six in the dioctahedral and trioctahedral smectites, respectively, with respect to the values calculated in the non‐homoionic samples. This change was not limited to the octahedral sheet and interlayer, because the tetrahedral content also changed. For both dioctahedral and trioctahedral samples, the structural formulae improved considerably after homoionization of the samples, although higher accuracy was obtained the more magnesic and trioctahedral the smectites were. Additionally, the changes in the structural formulae sometimes resulted in changing the classification of the smectite. [ABSTRACT FROM AUTHOR]

Many studies have shown that smectites, particularly under the effect of drying, could be one of the causes of the retrogradation of potassium (K) in the soil. Most of these studies have focused on the fi xation of K in montmorillonites with an octahedral charge deficit. However, smectites most often have both tetrahedral and octahedral charge deficits. This led us to study the variation in K exchangeability for a K-beidellite during wetting and drying (WD) treatment. Chemical analysis and X-ray diffraction showed that, the fine fraction of the studied raw clay is a mixed beidellite, where 70% of the charge comes from substitution in the tetrahedral layer. The study in the variation of K exchange capacity for K-beidellite as a function of the number of WD cycles, allowed to show that the amount of fixed K is related both to the number of WD cycles and to the negative charges arising from the substitution in the octahedral sheets. [ABSTRACT FROM AUTHOR]

The photoactive azobenzenes were intercalated into montmorillonite and beidellite in order to obtain a functional material responsive to UV radiation. The smectite modification involved two steps: (1) intercalation with alkylammonium salts, differing in alkyl chain length, and (2) co-intercalation with azobenzene or aminoazobenzene. The structure and chemistry of the obtained materials were thoroughly characterize with the means of XRD, FTIR, DTA/TG, UV–Vis methods and CHN elemental analysis. The mechanisms interpretation was supported with the molecular dynamics simulations. Photoresponse of the obtained materials was monitored through the observation of the basal spacing shifts upon UV radiation. The results proved that both the type of alkylammonium salt and the host mineral influenced heavily the efficiency of subsequent azobenzene intercalation as well as its photoactive behaviour. The evident and regular photoinduced basal spacing shifts were visible when the density of intercalated salts was low. This was achieved in the BId derivatives due to the low layer charge of the mineral. Also the shorter alkyl chain of the co-intercalated salt promoted larger photoresponses. [ABSTRACT FROM AUTHOR]

A review and a synthesis of the geological, mineralogical, and crystal chemical data available in the literature on active Spanish bentonitic exploitations were done, and at the same time, new data are provided from a set of representative samples from these deposits. They were located in three different areas with different geological origins: (1) Miocene sedimentary deposits from the Tajo Basin (Madrid−Toledo provinces) in the center of the Iberian Peninsula, where bentonites appear in two different units named for their colors (Green Clays and Pink Clays); (2) samples from Tamame de Sayago (Zamora province) originating from the hydrothermal alteration of granitic Variscan rocks; and 3) Miocene deposits originating from the hydrothermal alteration of volcanic or subvolcanic rocks from the Cabo de Gata volcanic area (Almería Province) in the southern part of Spain, where the three main deposits (Cortijo de Archidona, Los Trancos, and Morrón de Mateo) were studied. The bentonites from the Tajo Basin were formed mainly by trioctahedral smectites, and there were significant mineralogical differences between the Green and Pink Clays, both in terms of the contents of impurities and in terms of smectite crystallochemistry and crystallinity. The smectites from Tamame de Sayago were dioctahedral (montmorillonite−beidellite series), and they appeared with kaolinite, quartz, and mica in all possible proportions, from almost pure bentonite to kaolin. Finally, the compositions of the bentonites from the three studied deposits in Cabo de Gata were quite similar, and zeolites and plagioclases were the main impurities. The structural formulae of the smectites from Cortijo de Archidona and Los Trancos showed a continuous compositional variation in beidellite−montmorillonite, while in Morrón de Mateo, the smectites were mainly montmorillonite, although there was continuous compositional variation from Al montmorillonites to Fe−Mg-rich saponites. The variation in the smectite composition is due to the intrusion of a volcanic dome, which brings new fluids that alter the initial composition of the smectites.

Natural aluminosilicates can contain Fe in tetrahedral or octahedral coordination. Amongst smectites, tetrahedral iron is known to occur in Fe-rich nontronites but few indications exist for the presence of tetrahedral Fe in smectites of the montmorillonite--beidellite series. A set of 38 different bentonites showed a correlation of tetrahedral charge and Fe content in their smectites. All materials with large tetrahedral charge were rich in Fe. This could be explained by a general tendency of Fe to enter the tetrahedral sheet. To investigate this correlation, nine materials were selected and investigated by Mössbauer, UV-Vis, Fe K pre-edge and EXAFS spectroscopy with respect to tetrahedral Fe (Fe[IV]). The latter two methods were at the detection limit but Mössbauer and UV-Vis spectroscopy provided consistent results indicating the significance of both methods in spite of some scatter caused by the overall small amount of tetrahedral Fe. The results indicate the absence of any relation between Fe content and tetrahedral Fe. Tetrahedral Fe can be present in Fe-poor smectites and absent in the case of Fe-rich materials. This means that Fe-rich montmorillonites have a larger tetrahedral charge which is not caused by Fe[IV] but by Al[IV]. A possible explanation for this indirect relation is based on: the coordination of Al3+ in the weathering/smectite-forming solutions determines the coordination in the precipitates; and the Al[IV/VI] ratio increases with increasing pH. The correlation could thus be explained if the pH of weathering solutions generally was higher in Fe-rich parent smectite rocks than in more acidic smectite parent rocks. The relation between tetrahedral charge and Fe content can probably be explained by different geochemical contexts throughout the formation of smectites which affect the coordination of dissolved Al. [ABSTRACT FROM AUTHOR]

Além dos baixos teores normalmente encontrados na fração argila dos solos sob clima tropical e subtropical, o tamanho reduzido e a baixa cristalinidade dos minerais 2:1 secundários dificultam sua identificação por difratometria de raios X (DRX). Este estudo objetivou avaliar métodos químicos e físico de concentração de minerais 2:1 secundários na fração argila para facilitar a identificação por DRX, incluindo a natureza dos minerais quanto ao local de formação de cargas permanentes (lâmina tetraedral ou octaedral). Coletaram-se amostras de dois Cambissolos originados de argilito da Formação Guabirotuba na Bacia Sedimentar de Curitiba (PR): horizontes A, Bi, C1 (1,2 a 1,5 m), C2 (2,2 a 2,5 m), C3 (3,2 a 3,5 m) e C4 (4,2 a 4,5 m). Após remoção da matéria orgânica e dispersão da terra fina seca ao ar, a fração argila foi submetida a tratamentos sequenciais com ditionito-citratobicarbonato (DCB) (amostra desferrificada - remoção de óxidos de Fe pedogenéticos) e com soluções de NaOH a quente, em diferentes concentrações (0,5; 1,0; 1,5; 2,5; 3,5; 4,0; 4,5 e 5,0 mol L-1), para extração de gibbsita e caulinita, em diferentes graus. A fração argila desferrificada também foi submetida à separação física (centrifugação) em argila grossa (0,2 a 2 m) e fina (< 0,2 m). Foram realizados tratamentos auxiliares para identificar as espécies minerais 2:1 na fração argila: saturação com Mg e solvatação com etilenoglicol; saturação com K e secagem ao ar e aquecimento a 550 ºC; e saturação com Li (teste de Greene-Kelly). Os resultados mostraram que o método clássico de extração da caulinita, com solução de NaOH 5,0 mol L-1 a quente, não deve ser aplicado para concentração de minerais 2:1 secundários, pois também removeu grande parte desses minerais. O tratamento com DCB e com solução de NaOH 3,5 mol L-1 possibilitou, com maior eficiência, a concentração e identificação de minerais 2:1 secundários por DRX nas amostras dos horizontes A, Bi e C1. Nas amostras tomadas em maiores profundidades (horizontes C2, C3 e C4), devido aos maiores teores desses minerais e ao menor tamanho dos cristais (argila fina), a solução menos concentrada de NaOH (1,5 mol L-1) foi mais eficiente para esse propósito. No horizonte A, os minerais 2:1 concentraram-se na fração argila grossa, compatível com o maior grau de intemperismo desse horizonte. Identificou-se esmectita com hidroxi-Al entrecamadas nos horizontes mais superficiais (A e Bi) e esmectita nas amostras do horizonte C. A saturação com Li permitiu a identificação das esmectitas dioctaedrais montmorilonita e beidelita/nontronita. As adaptações ao métodopadrão (NaOH 5 mol L-1) favoreceram a concentração de minerais 2:1 secundários na fração argila dos solos; a concentração da solução de NaOH deve ser maior para horizontes com menor teor do mineral.Besides the typically low levels of secondary 2:1 minerals found in the clay fraction of soils in tropical and subtropical climates, the small mineral size and low crystallinity make their analyses by X-ray difractometry (XRD) difficult. This study aimed to evaluate physical and chemical methods for concentrating secondary 2:1 minerals in the clay fraction to facilitate their identification by XRD. Also, it was sought to analyze the nature of the minerals regarding the sites of origin of permanent charges (tetrahedral or octahedral sheets). Samples were collected in two Cambisols originated from argillite of the Guabirotuba formation in the sedimentary basin of Curitiba (PR), Brazil, in the horizons: A, Bi, C1 (1.2 to 1.5 m), C2 (2.2 to 2.5 m), C3 (3.2 to 3.5 m) and C4 (4.2 to 4.5 m). After removing the organic matter and dispersing the airdried fine earth, the clay was sequentially treated with dithionite-citrate-bicarbonate (DCB) (iron-free sample - removal of pedogenetic iron oxides) and with hot NaOH solutions at different concentrations (0.5, 1.0, 1.5, 2.5, 3.5, 4.0, 4.5, and 5.0 mol L-1) for kaolinite and gibbsite extraction at different degrees. The iron-free clay fraction was also physically separated (centrifugation) in coarse (0.2 to 2 µm) and fine clay (< 0.2 µm). Secondary treatments were performed to identify the 2:1 mineral species in the clay fraction: saturation with Mg and solvation with ethylene glycol, K saturation, air-drying and heating to 550 ºC; and Li saturation (Greene-Kelly test). Results showed that the classical method of kaolinite extraction with hot 5.0 mol L-1NaOH solution should not be used to concentrate secondary 2:1 minerals because the solution also removed a large portion of these minerals. The treatment with DCB and with 3.5 mol L-1NaOH solution was more efficient to concentrate and favored the identification of secondary 2:1 minerals by XRD in samples of the A, Bi and C1 horizons. In samples from greater soil depths (C2, C3 and C4 horizons), due to the higher levels of these minerals and the smaller crystal size (fine clay), a less concentrated NaOH solution (1.5 mol L-1) was more efficient for this purpose. In A horizon, 2:1 minerals were concentrated in the coarse clay fraction, what is compatible with the higher weathering degree of this horizon. Smectite with Al-hydroxy interlayers was identified in most surface horizons (A and Bi) and smectite was found in the C horizon samples. Li saturation made the identification of dioctaedral minerals (montmorillonite and beidellite/nontronite) possible. The modification of the standard method (5 mol L-1NaOH) favored the concentration of secondary 2:1 minerals in the soil clay fraction; the concentration of the NaOH solution must be higher for horizons with lower mineral content.

Swelling pressure of dioctahedral smectites in the montmorillonite – beidellite series was investigated by molecular dynamics simulations. The pressure was found to correlate inversely with the magnitude of the layer charge in the range of −0.5 to −1.0 per unit cell. The beidellite type smectites were found to have lower swelling pressure than the montmorillonite type smectites. A clear effect of the type of interlayer cations on the swelling pressure was found. The sodium smectites sustained significant pressure even at longer interlayer distances, while in calcium smectites the pressure decreased soon after the initial swelling. The simulation results are in good agreement with experimental observations and provide a tool for predicting macroscopic swelling behavior in smectites. [ABSTRACT FROM AUTHOR]

Five-membered cyclic organic carbonates (COC) are of interest for their ability to modify the surface properties of smectites and enhance the hydraulic resistance of bentonites to saline leachates. The mechanism of interaction of glycerol carbonate (GC) and several other hydroxyl containing cyclic organic carbonates (generally having progressively greater molecular masses) with sodium montmorillonite (Na + -Mt) was studied using powder X-ray diffraction and infrared spectroscopy. The 001 reflection for GC/Na + -Mt intercalates varied with the amount COC added, and the measured d 001 value increased from 1.29 nm to as large as 2.22 nm at equal-mass coverage of the COC to Na + -Mt. In general, when intercalated, the cyclic carbonyl (C O) stretch and the fundamental hydroxyl (O–H) stretch bands of COC derivatives were red-shifted with respect to these bands for neat COC, indicating strong ion-dipole interaction of the carbonyl group with interlayer Na + , and H-bonding of the OH group with both interlayer water and Mt surfaces. A stable and highly ordered intercalate was produced at a 1:1 mass loading with Mt in which about 6 GC molecules per unit cell (~ 7 molecules per Na + ion) replaced most of the interlayer water. [ABSTRACT FROM AUTHOR]

Smectites are clay minerals of interest due to their natural availability, extraordinary surface properties, and high swelling capacity in the presence of water. The behaviour of smectites and other layered phyllosilicates is largely affected by the appearance of isomorphous substitutions with a lower nuclear charge in their layer structures. These substitutions are the origin of negative net layer charge, and their distribution in the mineral layer impacts on the electrostatic properties of the mineral surfaces. The present density functional theory study shows that octahedral Mg(II) and tetrahedral Al(III) substitutions in aluminium-rich dioctahedral smectites tend to avoid each other and disperse in the layer structure. This behaviour is explained and demonstrated to originate from geometry deformations around the substitutions which are larger than the unsubstituted species. [ABSTRACT FROM AUTHOR]

We report an FPMD (first-principles molecular dynamics) study of the interfacial structures and acidity constants of the edge surfaces of ferruginous smectites. To understand the effects of Fe oxidation states on the interfacial properties, we investigated both the oxidized and reduced states of the (0 1 0)-type edges of two clay models with different Fe contents. The coordination states of edge Fe atoms are determined from the free energy curves for the desorption of the H 2 O ligands. The results of both clay models show that for Fe(III), only the 6-coordinate states are stable, whereas for Fe(II), both the 6- and 5-coordinate states are stable. Using the FPMD-based vertical energy gap technique, the p K a values of the edge sites are evaluated for both oxidation states. The results indicate that for both clay models, both the octahedral and tetrahedral sites become much less acidic upon Fe reduction. Therefore, the comparison reveals that the interfacial structures and protonation states are strongly dependent on the Fe oxidation states. Using the calculated results, we have derived the pH-dependent surface complexing mechanisms of ferruginous smectites. [ABSTRACT FROM AUTHOR]

This study aims at determining suitable conditions for the preparation of the best organobeidellite starting material used for the development of efficient mesoporous TiO 2 supported beidellite (Bd) photocatalysts. For this purpose, organo-modifications of natural Bd from Agadir Basin (Morocco) were achieved. The influence of (i) the length of alkyl chains C n (n = 8, 12, 14 and 16) of n-alkyl ammonium surfactants CH 3 (CH 2 ) n-1 NH 3 + and (ii) the amount of C 16 surfactant ranging from 1 to 5 times the smectite (Sm) cation exchange capacity (CEC) on the structure of organo- Bd was studied. XRD, TEM, TG-DTA and FTIR results are consistent with the intercalation of cationic surfactants species in Bd interlayer spaces according to different conformations yielding to their expansion. The interlayer expansion magnitude increased both with the length of alkyl chain and the amount of C 16 surfactant. Organomodification with increasing surfactant load beyond 1CEC besides yielded to the adsorption of increasing excess on external surfaces of Bd particles. These controlled structural modifications will be used further in the functionalization of this Bd by TiO 2 nanoparticles to produce efficient supported TiO 2 -Bd photocatalysts. [ABSTRACT FROM AUTHOR]

In this study, an Al-pillared smectite was synthesized and changes in its colloidal properties were investigated. The pillaring solution was prepared by mixing 0.4 mol L−1NaOH and 0.2 mol L−1AlCl3.6H2O solutions. Intercalated clays were heated to obtain the pillared clay, and X-ray diffractometry (XRD), X-ray fluorescence (XRF), Fourier transform infrared (FTIR) spectroscopy and N2sorption/desorption isotherms analysis were done to characterize the changes in clay properties. Moreover, adsorption experiments were carried out in order to evaluate the capacity of the pillared clays to remove Cu2+from an aqueous solution and to characterize the interaction between adsorbent and adsorbate. The results indicate that the natural clay has a basal spacing of 1.26 nm, whereas the pillared clays reached 1.78 nm (500°C) and 1.80 nm (350°C) after calcination. XRF analysis revealed an increase in the Al3+in the pillared clay as compared to the natural clay. The surface area and pore volume (micro and mesoporous) were higher for the pillared clays. Experimental data from the adsorption experiment were fit to Langmuir and Freundlich and Temkin adsorption models, and the former one was the best fit (highestr2value) for all the clays and lower standard deviation (Δg%) for the natural clay. On the other hand, the Temkin model exhibited Δg% value lower for the pillared clays. Thermodynamics parameters demonstrate that the Cu2+adsorption process is spontaneous for all the clays, but with higher values for the pillared materials. In addition, application of the Dubinin–Radushkevich model revealed that the bond between the metal and the clay are weak, characterizing a physisorption. [ABSTRACT FROM PUBLISHER]

Molecular simulations were performed to determine the structure and behavior of methane hydrate complexes in the interlayer of Na-rich montmorillonite and beidellite smectite. Molecular dynamics (MD) simulations used NPT ensembles in a 4 x 4 x 1 supercell comprised of montmorillonite or beidellite with methane hydrate complexes in the interlayer. The simulations presented here are in agreement with experimental data that show a significantly expanded interlayer (Guggenheim and Koster van Groos 2003; Koster van Groos and Guggenheim 2009). The smectite 2:1 layer forms part of the coordination sphere enclosing methane molecules; the MD results show that water molecules close to the siloxane surface form mixed cages that enclose methane molecules between basal oxygen atoms of the silicate rings and water molecules from the hydrogen bonding network. However, the higher tetrahedral charge did not favor the formation of methane hydrate components in the interlayer. Thus, methane hydrate complexes can be formed in pure montmorillonite more easily than in beidellite. Clay minerals obtained from marine localities with associated methane seeps and with variable Na, K, Ca, and Mg interlayer compositions were used to examine how swelling capacity affects the crystallization of smectite-methane-hydrate complexes. Results show that the formation of these complexes depends on the swelling capacity in the smectite. In samples with limited swelling properties, methane hydrate is formed in the pore spaces between particles and on the external surface of clays. [ABSTRACT FROM AUTHOR]

Abstract: Pillared clays (PILCs) based on bentonite clay from “Bogovina” (Serbia) were obtained using Al3+ and Fe3+ pillaring cations in different ratios. Thorough characterization of the starting material and PILCs was performed for better understanding of the catalytic activity that they had exibited in the catalytic wet peroxide oxidation (CWPO) of organic pollutants in water. The characterization consisted of the following techniques: XRD, XRD of oriented samples (swelling test), Greene-Kelley test (smectite type determination), TGA/DTA followed by XRD analysis of samples heated at characteristic temperatures, elemental analysis using ICP-OES and microwave digestion, FTIR, DR UV–Vis, Mössbauer spectroscopy, nitrogen physisorption at −196°C and SEM imaging. Smectite in admixture with quartz was identified, together with impurities like feldspar, illite, chlorite and X-ray amorphous matter. Smectite mineral was dominantly of the beidellite type. Pillaring led to changes in the d 001 smectite basal spacing and stabilization of the smectite structure. Increasing Fe3+ content of the pillaring solutions resulted in the increased incorporation of iron into the PILCs as isolated octahedrally coordinated Fe3+ cations, smaller and bigger oligonuclear octahedrally coordinated Fe3+ species and octahedrally coordinated Fe3+ particles. The structure of incorporated pillars was similar to that of naturally occurring minerals akageneite and lepidocrocite. Micro- and mesoporosity were improved due to pillaring and the layered smectite structure was retained. [Copyright &y& Elsevier]

Abstract: The thermodynamic properties of three aluminous 2:1 clay minerals were acquired at 1.013 bars and at temperatures between 5 and 500K using various calorimetric methods. Calorimetric measurements were performed on hydrated and dehydrated <2μm clay fractions of smectite MX-80 (Wyoming), illite IMt-2 (Silver Hill) and beidellite SBId-1 (Black Jack Mine). After purification, the mineralogical analyses gave the following structural formulae: and for smectite MX-80, illite IMt-2 and beidellite SBId-1, respectively. Heat capacities were measured by low temperature adiabatic calorimetry and differential scanning calorimetry, from 5 to 500K. Standard enthalpies of formation were obtained from solution–reaction calorimetry at 298.15K. The standard Gibbs free energies of formation of the clay minerals were also calculated, together with the equilibrium constants at 25°C, for anhydrous and hydrated minerals. A comparison between these experimental data and estimated values obtained from prediction models available in the literature, enabled the calculation method that appears to be the most relevant to be selected, at least for aluminous 2:1 clay minerals. [Copyright &y& Elsevier]

Abstract: The hydrothermal synthesis of smectites in the Al–Fe3+ chemical series was investigated at various pHs and temperatures using stoichiometric coprecipitated hydrogels. For the first time, Al–Fe3+ smectites within a wide compositional range were successfully synthesized. The windows of experimental conditions to crystallize such smectites are narrow. Temperatures up to 150°C and high pH (around 12) are suitable for the formation of the Fe3+-rich smectitic end-member (nontronite), while higher temperatures (200°C) and lower pH (down to 7) are suitable for the more Al-rich smectites (Fe3+-beidellites). For intermediary compositions, the pH and temperature of synthesis leading to pure smectite crystallization should be concomitantly adjusted. Outside these windows, admixtures or other phases are obtained. This is probably the reason why smectites of the beidellite–nontronite series were not extensively synthesized previously. [Copyright &y& Elsevier]

Abstract: Fe-rich kaolins in soils of a terrace chronosequence in the moist tropics of Costa Rica are derived from the transformation of smectite via interstratified kaolin–smectite (K–S). The smectite is ferruginous smectite (10.1±3.7% Fe2O3) that forms early during pedogenesis from basaltic–andesitic parent material and is the dominant mineral in <5 ka soils. Interstratified K–S with 60–90% kaolin layers is the dominant mineral in 10 ka soils, while 125 ka soils contain a physical mixture of Fe–kaolin (6.0±1.9% Fe2O3) and K–S with >80% kaolin layers. K–S is indicated by X-ray diffraction (XRD) data that reveal asymmetric 001 peaks between 17.5 and 17.8 Å (ethylene glycol-solvated) and irrational 00l peaks that exhibit Méring-like behaviour, and by transmission electron microscopy–analytical electron microscopy (TEM–AEM) data that document single crystals of K–S with compositions intermediate to those of end-member crystals of smectite and kaolin. Lattice fringe images from high resolution TEM (HRTEM) show lateral transitions from smectite layers to kaolin layers via a cell-preserved, layer-by-layer transformation mechanism, and changes in the compositions of tetrahedral and octahedral sheets, notably decreases in octahedral Fe and Mg and tetrahedral Al, indicate that the reaction is accompanied by localized dissolution of smectite 2:1 layers that proceeds laterally. Fourier transform infrared (FTIR) and XRD data indicate that kaolin layers are a mixture of kaolinite and halloysite, and differential thermal analysis–thermogravimetry (DTA–TG) combined with data from XRD and TEM–AEM indicate the development of Al-hydroxy-interlayers in K–S with time. The soil-forming factors that appear to control formation of K–S are (1) basaltic–andesitic parent that produces high concentrations of base cations and Si in young (<5 ka) soils, and (2) moist tropical climate (3085 mm MAP, 27.3 °C MAT) with a short dry season that fosters formation of smectite in <5 ka soils. By 125 ka, soils are dominated by Fe–kaolin and K–S, helping to constrain reaction rate. The relatively high cation exchange capacity (CEC) of the Fe-rich kaolins (18±12 cmolc/kg) relative to many tropical kaolinites is attributed to small amounts of octahedral Mg and tetrahedral Al inherited from precursor ferruginous smectite layers. Accordingly, the origin (from smectite) and relatively high CEC of the K–S and Fe–kaolin has potentially important implications related to clay mineral reactions and elemental cycling in moist tropical soils. [Copyright &y& Elsevier]

Abstract: The surface energy of some clays belonging to the smectite group has been calculated starting from crystal structures and combining a partial charge model with the computation of the lattice energy. The dioctahedral smectites studied here include montmorillonite; beidellites; and nontronite. One of the differences between these clays is the location of the substitution in the octahedral sheet or in the tetrahedral one. Another is the possibility of vacancies in cis- or trans-octahedral positions. These locations and vacancies have an effect on the distortion of the crystal framework and therefore on the surface energy. Calculated surface energies of the solid samples increase in the order beidellites > montmorillonite > nontronite. The bond energy between the interlayer cation and the layer appears to follow the same order and to depend both on the nature of the most electropositive elements of the layer and on their location. The trends obtained provide elements for an analysis of data related to interlayer enlargement. [Copyright &y& Elsevier]

Abstract: Amine-terminated hyperbranched poly(amine-ester)(HBP) dendrimer synthesized in our laboratory was used as a complex agent of the lanthanum(La3+) particles, and montmorillonite (MMT) as a stabilizer to gain HBP/La/MMT ternary nanocomposites. The results of TEM showed that HBP/La composites were deposited on the surface of the MMT layers within nanoscales. The sizes of clusters become larger and larger with the increase of MMT content. The information of DSC indicated that the T g of HBP/La/MMT nanocomposites with 5–30 wt.% MMT were increased significantly. [Copyright &y& Elsevier]

Abstract: In the current work, a sensitive, rapid and convenient electrochemical method was developed for the determination of Sudan I utilizing the excellent properties of montmorillonite calcium (MMT-Ca). Compared with the unmodified carbon paste electrode (CPE), MMT-Ca modified CPE not only significantly enhances the oxidation peak current of Sudan I but also lowers the oxidation overpotential, suggesting that the MMT-Ca modified CPE can remarkably improve the determining sensitivity of Sudan I. The experimental conditions such as determining medium, the content of MMT-Ca and accumulation time were optimized for the determination of Sudan I. The oxidation peak current is proportional to the concentration of Sudan I over the range from 0.05mgL−1 (2.01×10−7 mol L−1) to 1.0mgL−1 (4.03×10−6 mol L−1), and the limit of detection is 0.02 mg L−1 (8.06×10−8 mol L−1) for 2-min accumulation. Finally this newly-proposed sensing method was successfully employed to detect Sudan I in practical samples and good recovery was achieved. [Copyright &y& Elsevier]

Abstract: Tri-octahedral Li–Mg smectites (hectorites) were synthesized at temperatures ranging from 25 to 250°C, in the presence of solutions highly enriched in lithium. After removing all the exchangeable lithium from the synthesized clays, Li isotope fractionation (Δ7Liclay-solution) was determined. This fractionation was linked to Li incorporation into the structural octahedral site, substituting for Mg2+. As predicted, experimental Δ7Liclay-solution inversely correlates with temperature, and ranges from −1.6‰±1.3‰ at 250°C to −10.0‰±1.3‰ at 90°C, and then stays relatively constant down to 25°C. The relatively constant isotope fractionation factor below 90°C may be due to high concentrations of edge octahedra in low crystallinity smectites. The isotopic fractionation factor (α), for a given temperature, does not depend on the solution matrix, nor on the amount of structural Li incorporated into the clay. Empirical linear laws for α as a function of 1/T (K) were inferred. Smectite Li contents and smectite-solution distribution coefficients (D Li/Mg) increase with temperature, as expected for a substitution process. The fractions of dissolved Li incorporated into the smectite octahedral sites are small and do not depend on the duration of the experiment. In a seawater-like matrix solution, less Li is incorporated into the smectites, probably as a result of competition with dissolved Mg2+ ions for incorporation into the octahedral sites. The high Li contents observed in marine smectites are therefore best explained either by a significant contribution from basalts, by adsorption processes, or by the influence of seawater chemical composition on distribution coefficients. We also calculate, using present-day estimates of hydrothermal water and river fluxes, that a steady-state ocean would require a relatively large global clay-water Li isotope fractionation (−12‰ to −21‰). This study demonstrates the ability of laboratory experiments to quantify the impact of secondary phases on the Li geochemical cycle and associated isotope fractionations. [Copyright &y& Elsevier]

Abstract: Toluene isopropylation is carried out over modified montmorillonite clays. Effect of ion exchange and pillaring on the catalytic activity and selectivity is noted. Elemental analysis results give the extent of metal incorporated. Enhanced porosity is evident from X-ray diffraction as well as surface area – pore volume measurements. 29Si NMR shows the resonance for T (3Si, 1Al) units which shifts proportional to the amount of pillar metal present. Among the different modifications mixed metal oxide pillaring is found to be most effective in catalytic activity, p-cymene selectivity and lowering deactivation. [Copyright &y& Elsevier]

Abstract: Platinum sub colloids (nm range) were synthesized in the presence of a surfactant (CTAB) by micellar technique in which the metal particles ensured long-term stability in the aqueous dispersion and were prevented from agglomeration. When this surfactant stabilized Pt hydrosol was allowed to react with aqueous suspension of Na+ montmorillonite or Li+ hectorite, the cationic exchange reaction between Na+/Li+ and organic cation (CTA+) took place with simultaneous incorporation of the reduced Pt particles into the organoclay host. Finely divided and well-dispersed Pt particles (nm range) were generated by this method in the interlamellar space of the montmorillonite and hectorite. The catalyst samples with different metal loadings were synthesized and characterized with UV–Vis spectroscopy, XRD, TEM and AAS techniques. From the TEM micrographs it was confirmed that the diameter of the Pt particles intercalated was in the nanometer range. The catalytic activity of the synthesized catalysts was studied towards the selective hydrogenation of C cinnamaldehyde using a batch type high pressure reactor at different temperatures and hydrogen pressures. The catalytic activity of the catalysts and their selectivity towards cinnamyl alcohol were discussed in detail. The activity and selectivity of 1wt.% Pt loaded montmorillonite catalyst was found to be appreciable. [Copyright &y& Elsevier]

Abstract: Proton uptake on montmorillonite edge surfaces can control pore water pH, solute adsorption, dissolution kinetics and clay colloid behavior in engineered clay barriers and natural weathering environments. Knowledge of proton uptake reactions, however, is currently limited by strong discrepancies between reported montmorillonite titration data sets and by conflicting estimates of edge structure, reactivity and electrostatics. In the present study, we show that the apparent discrepancy between titration data sets results in large part from the widespread use of an erroneous assumption of zero specific net proton surface charge at the onset of titration. Using a novel simulation scheme involving a surface chemistry model to simulate both pretreatment and titration, we find that montmorillonite edge surface chemistry models that account for the “spillover” of electrostatic potential from basal onto edge surfaces and for the stabilization of deprotonated Alng sites through bond-length relaxation at the edge surface can reproduce key features of the best available experimental titration data (the influence of pretreatment conditions on experimental results, the absence of a point of zero salt effect, buffer capacity in the acidic pH range). However, no combination of current models of edge surface structure, reactivity and electrostatics can quantitatively predict, without fitted parameters, the experimental titration data over the entire range of pH (4.5 to 9) and ionic strength (0.001 to 0.5 mol dm−3) covered by available data. [Copyright &y& Elsevier]

Abstract: Two montmorillonites, an inorganic sodium montmorillonite (NaMMT) and an organo-modified montmorillonite (OMMT), were used for the preparation of montmorillonite/polypyrrole (MMT/PPy) composites. MMT particles were modified by the in situ polymerization of pyrrole in water, in aqueous solution of dodecylbenzenesulfonic acid (DBSA) used as anionic surfactant, and in water/methanol. Ferric chloride was used as oxidant in each case. Wide angle X-ray scattering (WAXS) measurements proved the intercalation of PPy into the galleries of NaMMT regardless the reaction media. In contrast, for OMMT/PPy composites, the increase of interlayer spacing depends on the preparation conditions, the highest increase in interlayer spacing was achieved in water/DBSA solution. The WAXS patterns of OMMT/PPy composites synthesized in methanol/water showed no change in interlayer spacing and the electrical conductivity of these composites was low, similar to that of NaMMT/PPy composites prepared under the same conditions. Conductivity about 1.1Scm−1 was reached for OMMT/PPy composites containing 13.3wt% PPy prepared in the presence of DBSA. The NaMMT/PPy composite containing 15.6wt% PPy and prepared under the same conditions showed a conductivity of 0.26Scm−1. X-ray photoelectron spectroscopy (XPS) proved that the surface of NaMMT/PPy composites is rich in MMT, whereas more PPy was found on the surface of OMMT/PPy composites. The conductivity of composites correlated with the N/Si atomic ratio determined from XPS results, which was taken as a semi-quantitative measure of the PPy surface fraction. [Copyright &y& Elsevier]

Abstract: Poly(vinyl alcohol)-based mixed matrix membranes loaded with 5 and 10wt.% of sodium montmorillonite (Na+MMT) clay particles, i.e. (PVA/Na+MMT-5 and PVA/Na+MMT-10), were fabricated by solvent casting method. The uncrosslinked membranes were used in pervaporation (PV) dehydration of aqueous solutions of isopropanol and 1,4-dioxane at 30°C. Membrane morphology was characterized by scanning electron microscopy. Differential scanning calorimetry, thermogravimetric analysis and dynamic mechanical thermal analysis were used to understand thermal properties. Universal testing machine was used to study mechanical strength properties. Separation factor to water has increased from 1116 to 2241 for PVA/Na+MMT-5 and PVA/Na+MMT-10 mixed matrix membranes when tested for 10wt.% water-containing isopropanol feed, but the corresponding flux values of 0.051 and 0.075kg/m2 h were somewhat lower than those observed for pristine PVA membrane. On the other hand, for water+1,4-dioxane feed mixtures, separation factors were quite lower and ranged from 216 to 369 with the corresponding flux values of 0.076 and 0.093kg/m2 h, respectively, for PVA/Na+MMT-5 and PVA/Na+MMT-10 membranes at 10wt.% water in the feed. Membranes of this study could extract up to 99.20 and 99.60wt.% water on the permeate side from water–isopropanol mixture, while from water–1,4-dioxane mixture, only 96.0 and 97.62wt.% of water were removed for 10wt.% water-containing feed. The membranes were further tested for PV at 40, 50 and 60°C for 10wt.% of water-containing feeds of aqueous isopropanol and 1,4-dioxane solutions to confirm their stability at higher temperatures. Plots of ln J p versus 1/T are linear in the studied range of 30–60°C for both the feed mixtures, indicating that flux follows an Arrhenius trend. PV results are discussed in terms of water flux, separation factor, permeation separation index, enrichment factor and activation energy of permeation. Sorption and PV experiments were carried out for the thermally crosslinked and glutaraldehyde crosslinked PVA/Na+MMT mixed matrix membranes for 10wt.% water-containing feed mixtures at 30°C. A small increase in separation factor with a slight sacrifice in flux was observed without showing any great difference as compared to uncrosslinked mixed matrix membranes. The hydrophilic nature of Na+MMT clay and the formation of PVA/Na+MMT mixed matrix membranes are responsible to offer such increased separation to water over the organic components of the feed mixtures. [Copyright &y& Elsevier]

Abstract: This paper represents an overview of the spectroscopic studies of both synthetic and naturally occurring beidellites performed as part of my research over the past 16 years. It shows that detailed information on the local structure of beidellite and changes in this local structure upon heating can be obtained by combining a range of spectroscopic techniques such as mid-infrared, near-infrared, infrared emission, Raman, nuclear magnetic resonance and X-ray photoelectron spectroscopy. [Copyright &y& Elsevier]

Atrazine (A) is one of the most applied herbicides and has a negative impact on the environment and health. Density functional theory (DFT) and experimental methods were used in the study of the immobilization of atrazine in two smectites, montmorillonite (Mt) and beidellite (Bd), as well as in their organically modified structures. Four systems were examined: A-Mt and A-Bd, as well as the structures modified by tetramethylphosphonium cation (TMP), A-TMP-Mt and A-TMP-Bd. The calculations revealed a flat arrangement of the atrazine in the interlayer space of both smectites with higher stability of beidellite structures. The presence of the TMP cation increased the fixation of atrazine in both organically modified smectites. The calculated vibrational spectra allowed a detailed analysis of the overlapping bands observed in the experimental FTIR spectra and their correct assignment. Further, selected FTIR bands unambiguously assigned to atrazine and both smectites served for the estimation of the adsorbed amount of atrazine. It was shown that the adsorption capacity of both TMP-modified smectites did not increase in comparison to the adsorption capacity of unmodified smectite samples. [ABSTRACT FROM AUTHOR]

Smectites affecting water and soil exchangeable cations, especially potassium and ammonium related to plants, are common swelling clay minerals in sediments and paleosols that can record paleoenvironmental and paleoclimatic information. Paleoenvironmental and paleoclimatic interpretations are potentially ambiguous, because smectite minerals may have either detrital or pedogenic origins. This study analyzes smectites in Lower Eocene paleosols of the Qaidam Basin, China, with the goal of determining their origin and paleoclimatic significance. Twelve smectite-rich vertisol samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), inductively coupled plasma-mass spectrometry (ICP-MS), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) in the Dahonggou (DHG) section of the Lulehe Formation. The samples from DHG section contained predominant dioctahedral smectites (60–65%) in the <2 μm clay fractions. Minor dioctahedral illites, dioctahedral interstratified illite-smectite (I-Sm), kaolinite, and traces of dioctahedral chlorites and palygorskites were present. The chemical data and FTIR spectra revealed both tetrahedral substitutions (i.e., Al for Si) and octahedral substitutions (i.e., Mg and minor Fe for Al) in the dioctahedral smectites. Montmorillonite comprised the dominance of the fine-clay fractions (< 0.2 μm) with minor contributions of beidellite, as determined by the Greene-Kelly test (GK-test), geochemical and FTIR analyses. SEM observations revealed two morphological types of dioctahedral smectites, the less abundant one with typical 'honeycomb' structure, interpreted as neoformed, and the other occurring as thin, well-defined plates and irregular masses considered to be detrital. DSC revealed two dehydroxylation temperatures (500–550 °C and 600–700 °C), indicating the presence of trans- vacant (t v) and cis- vacant (cv) layers, respectively. The cv layers were attributed to montmorillonite originating as catchment-delivered detritus, as the study Lulehe Formation exhibited no evidence of volcanic ash layers or diagenesis that would have promoted formation of montmorillonite with high dehydroxylation temperatures. The tv layers represented pedogenic beidellite formed via solution crystallization in a floodplain pedogenic environment. The accumulation of abundant inherited montmorillonite and neoformed beidellite in paleosols of the Lulehe Formation was probably promoted by a relatively warm climate with alternating wet-dry seasons during the Early Eocene. Admixture of detrital montmorillonite makes paleoclimatic reconstructions based on bulk-smectites concentrations and isotopic compositions unreliable, showing that integrated clay mineralogical analyses of the type undertaken in this study are necessary to identify the provenance and paleoclimatic significance of smectites in sediments. • Two subtypes of smectite, montmorillonite and beidellite, occur in Lulehe palesosols. • Predominant montmorillonite with high thermal ability has a detrital origin. • Minor beidellite with low dehydroxylation temperatures has a pedogenic origin. • Smectite accumulation/formation increased during EECO due to seasonal wet and dry. • Smectites in soils can be of multiple origin making their paleoenvironmental interpretation complex. [ABSTRACT FROM AUTHOR]

Chitosan-clay bionanocomposites were prepared from chitosan biopolymer solutions and four different smectites (SAz-1 and SWy-2 montmorillonites, SBId-1 beidellite and NAu-1 nontronite), and the effect of layer charge and charge distribution on the formation of bionanocomposites was examined. The intercalation of the chitosan in the homoionic Na+-smectite samples showed that all samples produced chitosan-smectite nanocomposites even at the lowest chitosan-clay ratios. The adsorption isotherms of chitosan by the smectites were classified as L- type isotherms. The equilibrium data were fitted to Langmuir and Freundlich isotherms and the equilibrium adsorption was best described by the Langmuir isotherm model for SWy-2 and SBId-1 while the Freundlich model achieved a better description for SAz-1 and NAu-1 for the higher chitosan concentrations. The adsorption of chitosan exceeded the CEC in the montmorillonites (SWy-2 and SAz-1) whereas in SBId-1 and NAu-1 with tetrahedral charge it either reached or it was lower than the CEC showing that layer charge and charge localization may hinder chitosan adsorption. Unlabelled Image • Chitosan-smectite bionanocomposites were produced even at the lowest chitosan-clay ratios. • Adsorption isotherms follow the Langmuir and the Freundlich model. • The increase of Δ d L spacing is in full accordance with adsorption isotherms. • Adsorption of chitosan in excess of the CEC is evident in smectites with octahedral charge. • Layer charge and charge localization influence chitosan adsorption and formation of bionanocomposites. [ABSTRACT FROM AUTHOR]

• Effect of iron on the swelling pressure of sodium smectites has been modeled. • The variables are dry density, total charge, charge location and iron content. • Increase in iron content results in decrease in the swelling pressure of smectites. • Effect is more pronounced in montmorillonite than beidellite at high dry densities. Smectites in bentonites contain variable amounts of iron substituting aluminum and silicon in the crystal structure. The swelling pressure of smectite models with varying Fe3+ content, layer charge and charge location were studied using molecular dynamics method. Swelling pressures decrease with increasing iron content at high dry densities, this is more pronounced in montmorillonites than beidellites with same layer charge. This swelling pressure decrease is slightly faster for smectites with lower layer charge. Results obtained from the study is useful in the screening process of iron-containing bentonites intended for use as sealants in High Level Radioactive Waste (HLRW) repositories. [ABSTRACT FROM AUTHOR]

A review and a synthesis of the geological, mineralogical, and crystal chemical data available in the literature on active Spanish bentonitic exploitations were done, and at the same time, new data are provided from a set of representative samples from these deposits. They were located in three different areas with different geological origins: (1) Miocene sedimentary deposits from the Tajo Basin (Madrid–Toledo provinces) in the center of the Iberian Peninsula, where bentonites appear in two different units named for their colors (Green Clays and Pink Clays); (2) samples from Tamame de Sayago (Zamora province) originating from the hydrothermal alteration of granitic Variscan rocks; and 3) Miocene deposits originating from the hydrothermal alteration of volcanic or subvolcanic rocks from the Cabo de Gata volcanic area (Almería Province) in the southern part of Spain, where the three main deposits (Cortijo de Archidona, Los Trancos, and Morrón de Mateo) were studied. The bentonites from the Tajo Basin were formed mainly by trioctahedral smectites, and there were significant mineralogical differences between the Green and Pink Clays, both in terms of the contents of impurities and in terms of smectite crystallochemistry and crystallinity. The smectites from Tamame de Sayago were dioctahedral (montmorillonite–beidellite series), and they appeared with kaolinite, quartz, and mica in all possible proportions, from almost pure bentonite to kaolin. Finally, the compositions of the bentonites from the three studied deposits in Cabo de Gata were quite similar, and zeolites and plagioclases were the main impurities. The structural formulae of the smectites from Cortijo de Archidona and Los Trancos showed a continuous compositional variation in beidellite–montmorillonite, while in Morrón de Mateo, the smectites were mainly montmorillonite, although there was continuous compositional variation from Al montmorillonites to Fe–Mg-rich saponites. The variation in the smectite composition is due to the intrusion of a volcanic dome, which brings new fluids that alter the initial composition of the smectites. [ABSTRACT FROM AUTHOR]