The reaction of benzene with exchangeable Cu(II) and Fe(III) in hectorite clay films was studied by electron paramagnetic resonance (EPR). The reaction when carried out in a sealed tube between 60° and 100°C produced a variety of organic radical products. The nature of these products depended on the concentration of water in the reaction medium and the reaction time. The free radicals were accompanied by a reduction in the oxidation state of the metal ions; this process had a zero-order dependence on the metal ion concentration. The activation energies determined from the zero-order rate constants are 67 ± 11 kJ/mole (Cu(II)) and 46 ± 6 kJ/mole (Fe(III)). The free radicals initially formed under anhydrous conditions appeared to populate sites in the interlayer region; the activation energies determined for this first order process are 57 ± 9 kJ/mole (Cu(II)) and 42 ± 3 kJ/mole (Fe(III)). These activation energies are within experimental error of those determined from the metal ion kinetics. The EPR signal due to organic radicals showed little temperature dependence; thus, exchange processes involving organic free radicals were probably not important in determining EPR lineshapes.

The nature of the siloxane surface in smectites was investigated by measuring the adsorption of aromatic hydrocarbons from water by organo-clays. The organo-clays were prepared by replacing the hydrophilic, inorganic exchange cations of a series of smectites with the small, hydrophobic organic cation, trimethylphenylammonium (TMPA). Smectites with a range in charge densities were used that resulted in different TMPA contents in the organo-clays. Adsorption isotherms of benzene, alkylbenzenes, and naphthalene from water by the TMPA-smectites indicated that sorption was inversely related to TMPA content. The Langmuir form of the isotherms suggests that the aromatic compounds adsorb to the clay surface. Possible adsorptive sites in TMPA-smectites are limited to the TMPA cations and the siloxane oxygen surfaces. Because sorption increased as layer charge and TMPA content decreased, the organic compounds must adsorb to the siloxane surfaces.

Calculations based on an adsorbed compound monolayer, which was estimated by fitting adsorption data to the Langmuir equation, and the N2 specific surface area of each TMPA-clay, indicate that the surface area occupied by each adsorbed molecule increases as the planar area of the molecule increases. This strongly indicates that the planar surfaces of the compounds adsorb directly to the clay surface. Apparently, the TMPA cations function to keep the smectite interlayers open. Interactions between the phenyl groups of TMPA cations on opposing interlayer clay surfaces may act to increase the size of the adsorptive regions. These results show that the siloxane surfaces of smectites can effectively adsorb aromatic hydrocarbons from water if the hydrophilic, inorganic exchange cations are replaced with small, hydrophobic organic cations. The strong adsorption of hydrophobic organic molecules from water demonstrates the hydrophobicity of the siloxane surfaces in smectites.

A high-charge smectite from Arizona [cation-exchange capacity (CEC) = 120 meq/100 g] and a low-charge smectite from Wyoming (CEC = 90 meq/100 g) were used to prepare homoionic tetra-methylammonium (TMA)-clay complexes. The adsorption of benzene, toluene, and o-xylene as vapors by the dry TMA-clays and as solutes from water by the wet TMA-clays was studied. The adsorption of the organic vapors by the dry TMA-smectite samples was strong and apparently consisted of interactions with both the aluminosilicate mineral surfaces and the TMA exchange ions in the interlayers. In the adsorption of organic vapors, the closer packing of TMA ions in the dry high-charge TMA-smectite, compared with the dry low-charge TMA-smectite, resulted in a somewhat higher degree of shape-selective adsorption of benzene, toluene, and xylene. In the presence of water, the adsorption capacities of both samples for the aromatic compounds were significantly reduced, although the uptake of benzene from water by the low-charge TMA-smectite was still substantial. This lower sorption capacity was accompanied by increased shape-selectivity for the aromatic compounds. The reduction in uptake and increased selectivity was much more pronounced for the water-saturated, high-charge TMA-smectite than for the low-charge TMA-smectite. Hydration of the TMA exchange ions and/or the mineral surfaces apparently reduced the accessibility of the aromatic molecules to interlamellar regions. The resulting water-induced sieving effect was greater for the high-charge TMA-smectite due to the higher density of exchanged TMA-ions. The low-charge Wyoming TMA-smectite was a highly effective adsorbent for removing benzene from water and may be useful for purifying benzene-contaminated water.

Montmorillonites saturated with small quaternary alkylammonium ions such as tetramethyl-ammonium (TMA) or trimethylphenylammonium (TMPA) are excellent sorbents for aromatic pollutants. In some cases, water inhibits arene sorption, but the inhibition mechanism is not understood completely. The objectives of this study were to determine whether arenes interact with adsorbed TMA and TMPA ions and/or with siloxane surfaces, and how water affects these interactions. We reacted benzene and ethylbenzene vapors with normal- and reduced-charge TMA- and TMPA-montmorillonite films at several relative humidities, and obtained infrared spectra of the resulting sorbate-clay complexes. Arene sorption caused the methyl asymmetric deformation vibrations adsorbed TMA and TMPA to shift to lower wave-number, whereas water sorption caused shifts to higher wavenumber. In the absence of water, benzene and ethylbenzene adsorbed on the siloxane surface as well as interacted directly with TMA and TMPA ions. The proportion of TMA and TMPA ions that interacted with benzene and ethylbenzene was greater for reduced-charge than normal-charge montmorillonite. Comparison of the HOH deformation and cation methyl asymmetric deformation vibrations indicated that both benzene and ethylbenzene inhibited water sorption substantially, and that water more readily displaced benzene and ethylbenzene from TMA and TMPA ions than from siloxane surfaces. Water inhibited arene sorption mainly by hydrating exchangeable cations, thereby obscuring siloxane surfaces adjacent to adsorbed TMA and TMPA ions and decreasing the average pore dimensions. These results indicate that in the presence of bulk water, arene adsorption likely occurs primarily on the siloxane surface.

The technique of scanning force microscopy (SFM) was used to study the nanometer-scale structure of Cu(II)-exchanged hectorite thin films. Supporting data were also obtained from Electron Spin Resonance (ESR) and X-ray diffraction (XRD) techniques. The surfaces studied included pure Cu(II)-exchanged hectorite, Cu(II)-exchanged hectorite exposed to benzene and Cu(II)-exchanged hectorite exposed to aniline. SFM images of the unexposed Cu(II)-exchanged hectorite surface revealed a smooth surface composed of interlocking platelets. The lateral dimension of these platelets ranged from a few nm to about 1 μm. After exposure to refluxing benzene, the SFM showed that the platelets underwent vertical shifts in position. This is believed to have occurred from intercalated benzene that polymerized in the interlayer region. No SFM evidence was obtained for benzene polymerization on the surface of the hectorite. Hectorite films exposed to aniline at room temperature revealed a post-polymerization structure on the hectorite surface consisting of small polymer bundles. The diameter of these bundles was measured to be 300–3000 Å, similar to the structure seen on electropolymerized polyaniline films. Aniline polymerized on the surface of hectorite films at 180 °C revealed a structure similar to undoped n-methyl-pyrrolidinone (NMP) cast polyaniline films. In this case, the polymer bundles are only 300 Å in dimension on average. XRD and ESR data also indicated interlayer aniline polymerization in Cu(II) exchanged hectorite. Mechanistic considerations affecting these polymerization reactions are presented.

The acidic properties of acid-modified montmorillonite and vermiculite were determined by pyridine and ammonia adsorption to correlate with the alkylating and dehydrating activity of the activated samples. Treatment of the minerals with different concentrations of hydrochloric acid results in the variation of overall acidity and density of acidic sites. Infrared (IR) spectral and differential scanning calorimetric analyses have revealed the presence of Bronsted and Lewis acid sites on the activated samples. The catalytic activity towards the above reaction has been correlated to the acid strength and density of Lewis acid sites. Treatment of montmorillonite with hydrochloric acid in the range of 0.1 and 0.3 M and vermiculite with 0.2 to 0.3 M seemed to be suitable for the conversion of methanol into olefin-rich hydrocarbons. Acid-activated montmorillonite catalyzed the isopropylation of benzene to a maximum extent of 16%, whereas acid-activated vermiculite gave a maximum conversion of only 4%.

The adsorption of 13C-labeled benzene on imogolite has been studied on samples which had been evacuated and then heated to remove water below their decomposition point. After adsorption of labeled benzene, the samples were studied by nuclear magnetic resonance using non-spinning techniques. The results show that benzene can occupy more than one pore type and that water does not displace benzene from the intra-tube pores at atmospheric pressure. A further finding is that there are at least two types of adsorbed benzene in so called inter-tube pores, one of which is more rigidly held than that in intratube pores. The presence of disordered materials at the edge of pores could also play a role in altering the pore mouth thereby creating new types of pores. Moreover, where two tubes do not pack properly, space might be created where an adsorbed molecule may bind more tightly than expected in a conventional pore.

A number of organobentonites were synthesized by exchanging the metal ions in bentonite with the cationic surfactant, cetyltrimethylammonium bromide. Samples of natural bentonite and organobentonites were analyzed for their organic carbon contents, examined by X-ray diffraction (XRD) for interlayer spacings, and viewed using a scanning electron microscope (SEM) for surface morphology. The sorption isotherm of benzene vapor from ambient air (relative humidity (RH) = 45 ± 5%) on natural bentonite was nonlinear; however, the isotherms of benzene from ambient air onto organobentonites were virtually linear over a large range of relative vapor concentrations. The sorption capacities of air-dried organobentonites were far greater than that of the natural bentonite. For air-dried organobentonites, the sorption coefficients correlated positively with the sample organic carbon contents and negatively with the sample BET-N2 surface areas. The heats of benzene vapor sorption onto air-dried organobentonites were less exothermic than the heat of benzene-vapor condensation. These findings suggest that benzene vapor sorption by air-dried organobentonites occurs essentially by vapor partition into the sample organic-matter fractions. This offers a potential application of organobentonites for the removal of organic vapors from flue gases and for assessing the efficiency of vapor removal.