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Montmorillonite (MMT) was converted to organoclays by intercalation of cationic surfactants into its interlayer space. Two types of organoclays were prepared from different surfactants (DDTMA and DDDMA) at different surfactant loadings, and the structural changes in the clays investigated using various techniques. The arrangements of surfactant molecules in the interlayer space was visually aided by molecular mechanical calculation (MM calculation), and the adsorption capacities of MMT and the organoclays for the removal of p-chlorophenol (PCP) and p-nitrophenol (PNP) from aqueous solutions were tested under different conditions. Two adsorption isotherm models (Langmuir and Freundlich isotherms) were used to determine the best fit model and the Freundlich isotherm was found to provide better fit for both PCP and PNP. Due to its hydrophobic properties, the adsorption is more favourable for PNP than PCP. Overall, the adsorption capacity of the organoclays was significantly improved by intercalation with large surfactant molecules as well as highly loaded surfactants as the intercalation with large surfactant molecules created the partitioning phase, which strongly attracted large amounts of organic pollutants. Possible mechanisms and the implications of the results for the use of these organoclays as adsorbents for the removal of phenols from the environment are discussed., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Modified montmorillonite was prepared at different surfactant (HDTMA) loadings through ion exchange. The conformational arrangement of the loaded surfactants within the interlayer space of MMT was obtained by computational modelling. The conformational change of surfactant molecules enhance the visual understanding of the results obtained from characterization methods such as XRD and surface analysis of the organoclays. Batch experiments were carried out for the adsorption of p-chlorophenol (PCP) and different conditions (pH and temperature) were used in order to determine the optimum sorption. For comparison purpose, the experiments were repeated under the same conditions for p-nitrophenol (PNP). Langmuir and Freundlich equations were applied to the adsorption isotherm of PCP and PNP. The Freundlich isotherm model was found to be the best fit for both of the phenolic compounds. This involved multilayer adsorptions in the adsorption process. In particular, the binding affinity value of PNP was higher than that of PCP and this is attributable to their hydrophobicities. The adsorption of the phenolic compounds by organoclays intercalated with highly loaded surfactants was markedly improved possibly due to the fact that the intercalated surfactant molecules within the interlayer space contribute to the partition phases, which result in greater adsorption of the organic pollutants., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Intercalation compounds of low- and high-defect kaolinites have been prepared by direct reaction with urea aqueous solution as well as by co-grinding with urea in the absence of water (mechanochemical intercalation). The complexes formed were studied by X-ray diffraction, thermal analysis, DRIFT spectroscopy, and scanning electron microscopy. In aqueous solution the degree of intercalation for the low- and high-defect kaolinites was found to be 77 and 65%, respectively. With mechanochemical intercalation, both kaolinites were almost fully expanded after 1 h of grinding. Based on the results of DRIFT spectroscopy, a structural model for the bonding of urea to the siloxane surface is proposed. The kaolinite-urea intercalation compounds produced by mechanochemical intercalation have crystallite sizes lower than those obtained by the aqueous solution method.

The mechanism for the decomposition of hydrotalcite remains unsolved. Controlled rate thermal analysis enables this decomposition pathway to be explored. Hydrotalcites containing carbonate, vanadate and molybdate were prepared by coprecipitation. The resulting materials were characterised by XRD, simultaneous TG-DTG-DTA and controlled rate thermal analysis (CRTA) to determine the stability and thermal decomposition pathway of the synthesised hydrotalcites. For the carbonate intercalated hydrotalcite dehydration takes place in three steps two of which are quasi-isothermal and one non-isothermal. Dehydroxylation and decarbonation occur separately over the 235-330 and 330-370 degrees C temperature range. A second non-isothermal decarbonation step is observed in the 371-541 degrees C range. In comparison the mixed carbonate-vanadate and carbonate-molybdate hydrotalcites show two dehydration steps and the dehydroxylation and decarbonation occur simultaneously. The observation of three dehydration steps is used to support the model of water molecules in three structurally distinct environments in the hydrotalcite interlayer. CRTA technology provides a mechanism for the decomposition of hydrotalcites.

The effect of mechanochemical activation (dry grinding), formamide intercalation, and thermal deintercalation on high- and low-defect kaolinite surfaces was studied by thermogravimetry and diffuse reflectance Fourier transform infrared spectroscopy. These investigations were completed with specific surface area and pore size distribution measurements. The surface acidity of the ground and the ground-and-intercalated kaolinites was probed with ammonia adsorption. The surface area and the pore volume as well as the amount of adsorbed ammonia increased with the rate of mechanochemical activation. At the same time the thermally deintercalated minerals showed increased surface area but decreased pore volume with the time of grinding. Adsorbed ammonia was detected as ammonium ion in the 1400-1500 cm(-1) spectral range.

The thermal behavior of a formamide-intercalated mechanochemically activated (dry-ground) kaolinite was investigated by thermogravimetry-mass spectrometry (TG-MS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFT). After the removal of adsorbed and intercalated formamide, a third type of bonded reagent was identified in the temperature range 230-350 degrees C decomposing in situ to CO and NH3. The presence of formamide decomposition products, as well as CO2 and various carbonates identified by DRIFT spectroscopy, indicates the formation of superactive centers as a result of mechanochemical activation and heat treatment (thermal deintercalation). The structural variance of surface species decreases with the increase of grinding time. The unground mineral contains a small amount of weakly acidic and basic centers. After 3 h of grinding, the number of acidic centers increases significantly, while on further grinding the superactive centers show increased basicity. With the increase of grinding time and treatment temperature the number of bicarbonate- and bidentate-type structures decreases in favor of the carboxylate- and monodentate-type ones.

A comparison is made of the mechanochemical activation of three low- and one high-defect kaolinite using a combination of X-ray diffraction, thermal analysis, and DRIFT spectroscopy. The effect of mechanochemical alteration of the kaolinites is greater for the low-defect kaolinites. The effectiveness of the mechanochemical treatment is represented by the slope of the d(001) peakwidth-grinding time line. High-defect kaolinite is not significantly altered by the grinding treatment. The effect of mechanochemical treatment on peakwidth was independent of the presence of quartz; the quartz acts as an additional grinding medium. The effectiveness of the mechanochemical treatment depends on the crystallinity of the kaolinite. Two processes are identified in the mechanochemical activation of the kaolinite: first the delamination of kaolinite appears to take place in the first hour of grinding and second a recombination process results in the reaggregation of the ground crystals. During this process proton hopping occurs and reaction to form water takes place. This water is then adsorbed and coordinated to surface-active sites created during mechanochemical treatment.

The effect of mechanochemical activation upon the intercalation of formamide into a high-defect kaolinite has been studied using a combination of X-ray diffraction, thermal analysis, and DRIFT spectroscopy. X-ray diffraction shows that the intensity of the d(001) spacing decreases with grinding time and that the intercalated high-defect kaolinite expands to 10.2 A. The intensity of the peak of the expanded phase of the formamide-intercalated kaolinite decreases with grinding time. Thermal analysis reveals that the evolution temperature of the adsorbed formamide and loss of the inserting molecule increases with increased grinding time. The temperature of the dehydroxylation of the formamide-intercalated high-defect kaolinite decreases from 495 to 470 degrees C with mechanochemical activation. Changes in the surface structure of the mechanochemically activated formamide-intercalated high-defect kaolinite were followed by DRIFT spectroscopy. Fundamentally the intensity of the high-defect kaolinite hydroxyl stretching bands decreases exponentially with grinding time and simultaneously the intensity of the bands attributed to the OH stretching vibrations of water increased. It is proposed that the mechanochemical activation of the high-defect kaolinite caused the conversion of the hydroxyls to water which coordinates the kaolinite surface. Significant changes in the infrared bands assigned to the hydroxyl deformation and amide stretching and bending modes were observed. The intensity decrease of these bands was exponentially related to the grinding time. The position of the amide C=O vibrational mode was found to be sensitive to grinding time. The effect of mechanochemical activation of the high-defect kaolinite reduces the capacity of the kaolinite to be intercalated with formamide.

Kaolinite surfaces were modified by mechanochemical treatment for periods of time up to 10 h. X-ray diffraction shows a steady decrease in intensity of the d(001) spacing with mechanochemical treatment, resulting in the delamination of the kaolinite and a subsequent decrease in crystallite size with grinding time. Thermogravimetric analyses show the dehydroxylation patterns of kaolinite are significantly modified. Changes in the molecular structure of the kaolinite surface hydroxyls were followed by infrared spectroscopy. Hydroxyls were lost after 10 h of grinding as evidenced by a decrease in intensity of the OH stretching vibrations at 3695 and 3619 cm(-1) and the deformation modes at 937 and 915 cm(-1). Concomitantly an increase in the hydroxyl stretching vibrations of water is found. The water-bending mode was observed at 1650 cm(-1), indicating that water is coordinating to the modified kaolinite surface. Changes in the surface structure of the OSiO units were reflected in the SiO stretching and OSiO bending vibrations. The decrease in intensity of the 1056 and 1034 cm(-1) bands attributed to kaolinite SiO stretching vibrations were concomitantly matched by the increase in intensity of additional bands at 1113 and 520 cm(-1) ascribed to the new mechanically synthesized kaolinite surface. Mechanochemical treatment of the kaolinite results in a new surface structure. Copyright 2001 Academic Press.

Controlled rate thermal analysis (CRTA) technology made possible the separation of adsorbed formamide from intercalated formamide in formamide-intercalated kaolinites. X-ray diffraction shows that the CRTA-treated formamide-intercalated kaolinites remain expanded after CRTA treatment. The Raman spectra of the CRTA-treated formamide-intercalated kaolinites are significantly different from those of the intercalated kaolinites with both intercalated and adsorbed formamide. An intense band is observed at 3629 cm(-1), attributed to the inner surface hydroxyls hydrogen bonded to the formamide. Broad bands are observed at 3600 and 3639 cm(-1) and are attributed to the inner surface hydroxyls, which are hydrogen bonded to the adsorbed water molecules. The hydroxyl stretching band of the inner hydroxyl is readily observed at 3621 cm(-1) in the Raman spectra of the CRTA-treated formamide-intercalated kaolinites. The results of thermal analysis show that the amount of intercalated formamide between the kaolinite layers is independent of the presence of water. The Raman bands of the formamide in the CRTA-treated intercalated kaolinites are readily observed. Copyright 2001 Academic Press.