Summary Thermo-XRD-analysis is applied to identify whether or not the adsorbed organic species penetrates into the interlayer space of the smectites mineral. In this technique an oriented smectite sample is gradually heated to temperatures above the irreversible dehydration of the clay, and after each thermal treatment is diffracted by X-ray at ambient conditions. In the thermal treatment of organo-clays, under air atmosphere at temperatures above 250°C, the organic matter is in part oxidized and charcoal is formed from the organic carbon. In inert atmosphere e.g. under vacuum above 250°C the organic matter is pyrolyzed and besides small molecules, charcoal is formed. If the adsorbed organic compound is located in the interlayer space, the charcoal is formed in that space, preventing the collapse of the clay. A basal spacing of above 1.12 nm suggests that during the adsorption the organic compound penetrated into the interlayer space. Thermo-XRD-analyses of montmorillonite complexes with anilines, fatty acids, alizarinate, protonated Congo red and of complexes of other smectites with acridine orange are described. To obtain information about spacings of the different tactoids that comprise the clay mixture, curve-fitting calculations on the X-ray diffractograms were adapted.
Thermogravimetric (TG) and differential thermal analysis (DTA) curves of methyltributylammonium smectite (MTBAS), methyltrioctylammonium
smectite (MTOAS), and di(hydrogenatedtallow)dimethylammonium smectite (DHTDMAS), and also corresponding sodium smectite (NaS)
and tetraalkylammonium chlorides (TAAC) were determined. The TAACs was decomposed exactly by heating up to 500°C. The adsorbed
water content of 8.0% in the pure NaS was decreased down to 0.2% depending on the size of the non-polar alkyl groups in the
tetraalkylammonium cations (TAA+). The thermal degradation of the organic partition nanophase formed between 2:1 layers of smectite occurs between 250–500°C.
Activation energies (E) of the thermal degradations in the MTBAS, MTOAS and DHTDMAS are 13.4, 21.9, and 43.5 kJ mol−1, respectively. The E value increases by increasing of the interlayer spacing along a curve depending on the size of the alkyl groups in the TAA+.
Authors:G. Rytwo, R. Huterer-Harari, S. Dultz, and Y. Gonen
of erythrosin-B (EB) and fast green (FG) to a non-charged organosmectite based
on crystal violet adsorbed up to 100% of the cation exchange capacity (CEC)
was tested. Adsorption isotherms of EB and FG were prepared at 3, 24 and 50C.
All isotherms are of H-type reaching loads of approximately up to 20% of the
original CEC of the crude montmorillonite (up to 0.15 and 0.10 mol dye kg–1
clay for EB and FG, respectively). Adsorption decreases with temperature,
indicating an exothermic process. Enthalpy was evaluated using van’t
Hoff equation, yielding approximately –20 kJ mol–1
for both dyes.
A sodium smectite (NaS) with a cation exchange capacity (CEC) of 1.08 mol kg−1 was intercalated with methyltributylammonium cation (MTBA+) with proportions equivalent to 0.2, 0.4, 0.6, 0.8 and 1.0 times the CEC. The contents of adsorbed water and intercalated
MTBA+ in the prepared organosmectites (OSs) were determined by using the differential thermal analysis (DTA) and thermogravimetry
(TG) curves. The adsorbed water of 8% in the NaS decreases greatly in OSs with the increase of the MTBA+ content and reduces to 2.0% for the 1.0 CEC sample. This explains the gradual change of the NaS from hydrophilic to hydrophobic
character. Thermal degradation of the intercalated MTBA+ in OSs occurs approximately between 250–450°C. The oxidation of the formed charcoal to CO2 occurs between 450–850°C. The intercalated MTBA+ content for each OS is obtained from both the TG and carbon analysis. The results do not agree exactly, but both the results
tend to increase by increasing initial content of the MTBA+ in solution.