The adsorption of the monovalent organic cations benzyltrimethylammonium (BTMA) and benzyltriethylammonium (BTEA) to montmorillonite was studied as a function of their concentrations and ionic strength. At low ionic strength the adsorbed amounts of BTMA and BTEA reached values of the cation exchange capacity (CEC) of the clay. An increase in the ionic strength resulted in reduction in the adsorbed amounts of the organic cations, unlike the pattern observed previously with organic monovalent cationic dyes. The reduction in adsorbed amounts of BTMA and BTEA depended on the inorganic cations according to the sequence Cs+ > Na+ > Li+, which follows the sequence of binding coefficients of these inorganic cations added. The type of the anion (that is, Cl−, ClO4−, SO42-) had no effect on the adsorbed amounts. An adsorption model which considers the electrostatic Gouy-Chapman equations, specific binding and closeness of the system could adequately simulate the adsorbed amounts of BTMA and BTEA and yield predictions for the effect of the ionic strength and concentration of electrolytes. The binding coefficient employed was K = 5000 M−1 for the formation of neutral complexes of BTMA and BTEA. This value is larger than those found for the inorganic cations but is several orders of magnitude below those found for the monovalent dyes. The binding coefficients for the formation of charged complexes of BTMA and BTEA were 20 and 5 M−1, respectively. The basal spacing of the clay did not change significantly with the adsorbed amounts of both BTMA and BTEA up to the CEC.

A low-charge Na-montmorillonite (SWy-2) was exchanged with hexadecyltrimethyl-ammonium (HDTMA) at levels equal to 20, 40, 60, 70, 80, 90, 100, 150 and 200% of the cation exchange capacity (819 mmol(+)/kg) to determine the nature of adsorption and the ionic composition of the clay interlayers. In contrast with earlier work with smaller aliphatic cations, which suggested random interstratification of interlayers occupied by either organic or metallic cations, there was no evidence of cation segregation into homogeneous interlayers. Instead, X-ray analysis indicated that the organic cations assumed two dominant configurations which were roughly equivalent in prevalence at ∼70% coverage of the CEC. Below 70% exchange the organocations existed predominantly in heterogeneous monolayers with Na+, attaining basal spacings of between 1.41 and 1.44 nm which were sensitive to changes in relative humidity. Relative humidity effects indicated that Na+ and HDTMA occupied functionally discrete domains within the interlayer as shown by the free interaction of water and a neutral organic solute, naphthalene, with Na+ and HDTMA, respectively. At greater levels of HDTMA exchange (up to 100% of the CEC), the organocations assumed a predominantly bilayer configuration. Transition to a fully-developed bilayer indicated by a 1.77 nm d-spacing at 100% coverage was gradual, suggesting some interstratification of the monolayers and bilayer configurations between 70 and 100% exchange. Sorption of naphthalene to the organoclays within this range of coverage was well correlated with clay organic carbon content, consistent with relatively unimpeded interlayer access of neutral organic molecules.

Al-hydroxy intercalated clays (ALHICs) obtained from different parent clays were used to investigate the interactions between oligomers and clay surface layers.

The thermal stability of ALHICs obtained from natural, Cs-, Ca-, Ba-, Fe-, Cu- or Ce-montmorillonites has been investigated by studying the relationship between basal spacing and calcination temperature. X-ray diffraction has shown that the basal spacing of ALHICs obtained from Cu-montmorillonite calcined at 550°C is 13.4 Å, different from basal spacings of ALHICs obtained from Fe-montmorillonite (16.0 Å) and other parent clays (16.7 Å). Thermograms for AlHICs obtained from natural, Fe- and Ce-montmorillonites displayed distinct steps at 225 and 650°C, attributed to the dehydration of Al13 oligomers, and the dehydroxylation of the surface layer, respectively. By contrast, thermograms of ALHICs obtained from Cu-montmorillonite displayed one step between 250 and 700°C for both dehydration and dehydroxylation. Mössbauer parameters showed that Fe3+ octahedra in octahedral sheets are distorted in pillared interlayered clay (PILC) obtained from Cu-montmorillonite and undistorted in that obtained from Fe-montmorillonite. The difference in thermal stability for the various ALHICs is attributed to the retention of some of the original cations after intercalation with Al13 oligomers, which induces several interactions between the oligomers and the clay surface layers.

The swelling property of smectite is dominated by the hydration of exchangeable cations in the interlayer spacing (‘interlayer hydration’). By investigating systematically the swelling behavior of various exchangeable cations with different valences and ionic radii, the interlayer hydration of smectite was explored. The swelling behavior of Li+-, K+-, Rb+-, Cs+-, Mg2+-, Sr2+-, Ba2+-, and La3+- montmorillonites in undersaturated conditions was measured precisely over the range 50–150°C by in situ X-ray diffraction (XRD) analyses. The systematic swelling behavior of ten homocationic montmorillonites, the aforementioned eight homoionic montmorillonites, plus Na+ and Ca2+ from a previous study, and the cation hydration energies were analysed by studying the changes occurring in the basal spacing and the 001 peak width. With decreasing cation hydration energy, swelling curves (i.e. plots of basal spacing vs. relative humidity (RH)) change from continuous (Mg2+, La3+, and Ca2+) to stepwise (Sr2+, Li+, Ba2+, and Na+) to one-layer only (K+, Rb+, and Cs+). For the first two groups, the RH at the midpoint between the one- and two-layer hydration states increased as the cation hydration energy decreased. Under low RH, with increasing temperature, the basal spacings of Mg-, La-, Ca-, Sr-, Li-, and Ba-montmorillonites decreased continuously to the zero-layer hydration state, whereas Na-, K-, Rb-, and Cs-montmorillonites swelled from the zero-layer hydration state even at the lowest temperature (50°C). A decrease in the basal spacing at the same RH but at different temperatures suggests the existence of metastable states or that the layer-stacking structure changes with temperature. The systematics of the swelling behavior of various homocationic montmorillonites as functions of RH and temperature (<150°C) at 1 atmare reported here.

Titanium was introduced into the clay structure by cation exchange with polymeric Ti cations which were formed by partial hydrolysis of Ti alkoxide in HCl. X-ray diffraction, N2 adsorption-desorption, chemical analysis, thermogravimetric analysis, differential thermal analysis, temperature-programmed desorption of ammonia and temperature-programmed reduction were used to characterize the resulting Ti-pillared clays (Ti-PILCs). Titanium methoxide allows the synthesis of a solid with a large basal spacing (26 Å), a large surface area (360 m2/g), a significant amount of micropore surface area (90%), and notable acidity. Moreover, Ti-PILCs obtained from methoxide were found to be thermally stable up to 500°C. A correlation between the increase in acidity and the increases in both microporosity and Ti content was observed. The surface area, the micropore volume, the acidity and the d001 peak intensity all increased upon increasing the amount of Ti added to the preparation (up to ∼15 mmoles of Ti/g clay). The use of an aqueous suspension of 0.13 wt.% of clay yielded the best structural and textural properties in terms of subsequent use of the clay as a catalyst.

Intercalation of montmorillonites with a mixture of intercalates has not been studied extensively. The objective of the present investigation was to study the effects of phosphonium-based intercalate mixtures on the properties (organic loading and basal spacing) of montmorillonite. These phosphonium-intercalated montmorillonites are promising candidates as high-temperature stable nanofillers for application in clay polymer nanocomposites.

Two salts with different cationic heads and chain lengths were mixed in varying molar ratios and the mixtures were intercalated into the interlayer space of montmorillonite. Two sets were chosen based on the chain length and the cationic head-group structure of the two intercalated salts (referred to hereafter as set 1 and set 2). The resultant intercalated montmorillonite was characterized by thermogravimetric analysis, X-ray diffraction, and transmission electron microscopy. The organic loading of the intercalated montmorillonite increased with the proportion of longer carbon-chain intercalate in the mixture. The intensity of the characteristic XRD peak of each intercalate varied with the mole fraction percent of that intercalate in the solution mixture. No marked synergistic effect of the intercalate mixture on the basal spacing and organic loading properties of the intercalated montmorillonite was observed — the proportional influence of individual components was found to be more prominent.

The effects of temperature on the swelling properties of smectites are important for a variety of different geological conditions, but studies on this topic have been rather limited. The purpose of this study was to investigate the swelling behavior of Na- and Ca-montmorillonite at various temperatures greater than room temperature, up to 150°C, using in situ X-ray diffraction (XRD) analysis. A sample chamber was designed, the temperature and humidity of which were controlled precisely, for environmental in situ measurements. The XRD measurements were performed at small relative humidity (RH) intervals for precise observation of the swelling behavior.

The swelling behavior of Na-montmorillonite showed distinct zero-, one-, and two-layer hydration states. The basal spacings of Na-montmorillonite changed continuously with RH for various temperatures in the transition region between the zero- and one-layer hydration states, and the swelling curves of the transition region moved to greater degrees of RH with increasing temperature. The basal spacings jumped from the one- to two-layer hydration states for all temperatures at almost the same RH.

The basal spacings of Ca-montmorillonite changed continuously from the zero- to the two-layer hydration states at all temperatures. This behavior is remarkably different from that of Na-montmorillonite. At low-RH conditions, the d001 value of Ca-montmorillonite decreased with increasing temperature. The swelling curves of Ca-montmorillonite did not show a plateau at any temperature for the one-layer hydration state. The swelling curves of Ca-montmorillonite moved to greater RH with temperature, similar to the transformation region between the zero- and one-layer hydration states in Na-montmorillonite. These differences between Na- and Ca-montmorillonite are related to the hydration powers of exchangeable cations.

Iron-pillared clays (Fe-PILCs) were synthesized from hydrolyzed FeCl3 solutions added to NaOH solutions using different synthesis conditions. X-ray diffraction, N2 adsorption-desorption, chemical analysis, thermogravimetric analysis, differential thermal analysis, temperature-programmed desorption of ammonia and temperature-programmed reduction were used to characterize the resulting Fe-pillared clays (Fe-PILCs). A higher degree of pillaring was obtained when the Fe content was adjusted to 60 mmoles of Fe/g of clay. It was observed that higher values of this ratio led to worse acidity and textural characteristics, a consequence of the probable formation of Fe oxides that could not only deposit on the surface but also block the pores formed during the pillaring process. Likewise, it was found that the amount of Fe that can be introduced depended on the OH/Fe ratios. Total surface and micropore area decreased and Fe content increased with increasing pillaring solution concentrations. Finally, all pillared samples prepared here were thermally stable at temperatures up to 400°C.

This work presents the water retention curves obtained for two natural bentonites compacted at different dry densities. The density of the bentonite was kept constant during the determination, for which specific methodologies were developed. The materials tested are the FEBEX and the MX-80 bentonites, in the first of which divalent cations (Ca and Mg) predominate in the exchange complex; MX-80 is mainly sodic. The water retention capacity of the FEBEX bentonite is greater, although the difference between both bentonites becomes smaller towards low suctions. The effect of dry density on the water retention curve is very small or imperceptible for suctions >10 MPa, and below this value the lower the density of the bentonite, the greater its water content. The basal spacing of the samples equilibrated at different suctions has been measured and found to be in the order of those measured by other authors in powder samples equilibrated to the same suctions. The study was performed in the framework of projects concerning the engineered bentonite barrier of high-level radioactive waste repositories.