Authors:Z. Malek, V. Balek, D. Garfinkel-Shweky, and S. Yariv
The dehydration and dehydroxylation of the smectites, beidellite and montmorillonite (dioctahedral) and saponite and laponite (trioctahedral), were investigated by ETA, DTA, TG and X-ray diffractions. There are differences between the behaviors of di- and trioctahedral clays which are due to the differences in the ability of the exchangeable cations to migrate into hexagonal holes of the SiO4 network and due to the fact that the dehydroxylation and recrystallization of dehydroxylated trioctahedral smectites occur simultaneously, whereas there is a temperature gap of about 300°C between the dehydroxylation and the recrystallization of dioctahedral smectites.
Authors:A. Nasser, M. Gal, Z. Gerstl, U. Mingelgrin, and S. Yariv
The adsorption of the tertiary aromatic amide alachlor by Na-montmorillonite and Al-polyhydroxy-montmorillonite was investigated
by DTA, XRD, SEM and Thermo-FTIR Spectroscopy. This molecule is adsorbed into the interlayer space of the montmorillonite,
replacing interlayer water. In this organo-clay complex the interlayer water forms hydrogen bonds with N or O atoms of the
tertiary amide group. Samples which were aged during six months degraded by hydrolysis to give mainly secondary amide. This
reaction was catalysed by Al-polyhydroxy-montmorillonite more than by Na-montmorillonite.
Authors:A. Landau, A. Zaban, I. Lapides, and S. Yariv
The mechanochemical solid-state adsorption of the cationic dye rhodamine-6G (R6G) by montmorillonite was investigated by XRD
and simultaneous DTA-TG. Five different mixtures of R6G and montmorillonite were investigated. They contained 10, 20, 35,
50 and 100 mmol R6G per 100 g clay. The solid R6G was ground with the clay for five minutes. Mixtures were ground both in
the absence of water (dry grinding) and with the adding of drops of water periodically, (wet grinding). There were no differences
between samples obtained by wet or dry grinding. X-ray and DTA data were compared with those of R6G-montmorillonite obtained
from aqueous suspensions. The mechanochemical products were different from those obtained from aqueous suspensions. The X-ray
and DTA studies suggest that the mechanochemical adsorption of organic cations takes place on the external surfaces of the
clay whereas in suspensions the adsorption takes place into the interlayer space. In the latter case the final stages of oxidation
occur in temperatures higher than those of the neat dye whereas in the former they occur at lower temperatures.
Authors:F. Burstein, M. Borisover, I. Lapides, and S. Yariv
In the present research we studied the effect of the solvent used, whether it was polar water or a non-polar organic solvent
(n-hexane or n-hexadecane), on the basal-spacing and bulk structure of the sorbate-sorbent complexes obtained by the secondary adsorption
of nitrobenzene and m-nitrophenol by two types of organo-montmorillonites. X-ray measured basal spacings before and after thermal treatments up
to 360°C. The organo-clays were synthesized, with 41 and 90% replacement of the exchangeable Na+ by hexadecyltrimethylammonium (HDTMA), with mono-and bilayers of HDTMA cations in the interlayer space, labelled OC-41 and
OC-90, respectively. After heating at 360°C both organo-clays showed spacing at 1.25–1.28 nm, due to the presence of interlayer-charcoal,
indicating that in the preheated organo-clays the HDTMA was located in the interlayer.
The thermo-XRD-analysis of Na-clay complexes showed that from organic solvents both sorbates were adsorbed on the external
surface but from water they were intercalated. m-Nitrophenol complexes of both organo-clays obtained in aqueous suspensions contain water molecules. Spacings of nitrobenzene
complexes of OC-41 and OC-90 and those of nitrophenol complexes of OC-41 showed that the adsorbed molecules were imbedded
in cavities in the HDTMA layers. Adsorption of m-nitrophenol by OC-90 from water and n-hexane resulted in an increase of basal spacing (0.21 and 0.29 nm, respectively) suggesting the existence of a layer of nitrophenol
molecules sandwiched between two parallel HDTMA layers.
Authors:S. Yariv, I. Lapides, K.H. Michaelian, and N. Lahav
Solid state intercalation of alkali halides into kaolinite takes place by heating pressed disks of dimethylsulfoxide (DMSO)-kaolinite
complex ground in different alkali halides. This reaction involves diffusion of the DMSO outside the interlayer space and
the alkali halide into the interlayer space. IR and Raman spectroscopy reveal two types of intercalation complexes: (i) almost
non-hydrous, obtained during thermal treatment of the DMSO complex; and (ii) hydrated, obtained by regrinding the disk in
air. The strength of the hydrogen bonds between intercalated water or halide anions and the inner surface hydroxyls decreases
in the order Cl−>Br−>I−. Chlorides penetrate the ditrigonal holes and form hydrogen bonds with the inner OH groups.
Authors:I. Lapides, N. Lahav, K. H. Michaelian, and S. Yariv
Intercalation complexes of kaolinite with a series of alkali halides (NaCl (trace amounts), KCl, RbCl, CsCl, NaBr, KBr, CsBr, Kl, Rbl and Csl) were obtained by a thermal solid state reaction between the kaolinite-dimethylsulfoxide intercalation complex and the appropriate alkali halide. The ground mixtures (1∶1 weight ratio) were pressed into disks that were gradually heated up to 250 °C for different times. X-ray diffractograms of the disks were recorded after each thermal treatment. At the end of the thermal treatment the disks were ground and basal spacings of the powders obtained. As a result of thermal treatment, alkali halide ions diffuse into the interlayers, replacing the intercalated dimethylsulfoxide molecules. Such a replacement may take place only if the thermal diffusion of the penetrating species is faster than the evolution of the intercalated organic molecule. With increasing temperature the intercalated salt diffused outside the interlayer space or underwent a thermal hydrolysis which resulted in the evolution of hydrogen halides from the interlayer space. Consequently, the amounts of intercalation complexes decreased at elevated temperatures.