Yariv, S., Institute of Chemistry, Hebrew University of Jerusalem, Edmund Y. Safra Campus, 91904 Jerusalem, Israel
Lapides, I., Institute of Chemistry, Hebrew University of Jerusalem, Edmund Y. Safra Campus, 91904 Jerusalem, Israel
Borisover, M., Institute of Soil, Water and Environmental Sciences, Volcani Center, POB 6, 50250 Bet Dagan, Israel

Na-montmorillonite was loaded with tetraethylammonium cations (TEA) or with benzyltrimethylammonium cations (BTMA) by replacing 77 and 81% of the exchangeable Na with TEA or BTMA, labeled TEA-MONT and BTMA-MONT, respectively. TEA- and BTMA-MONT were heated in air up to 900 °C. Thermally treated organoclays are used in our laboratory as sorbents of organic compounds from water. The two organoclays were studied by TG and DTG in air and under nitrogen. Carbon content in each of the heated sample was determined. They were diffracted by X-ray, and fitting calculations of d(001) peaks were performed on each diffractogram. TG and thermo-C analysis showed that at 150 and 250 °C both organoclays lost water but not intercalated ammonium cations. DTG peak of the first oxidation step of the organic cation with the formation of low-temperature stable charcoal (LTSC) appeared at 364 and 313 °C for TEA- and BTMA-MONT, respectively. The charcoal was gradually oxidized by air with further rise in temperature. DTG peak of the second oxidation step with the formation of high-temperature stable charcoal (HTSC) appeared at 397 and 380 °C for TEA- and BTMA-MONT, respectively. DTG peak of the final oxidation step of the organic matter appeared at 694 and 705 °C for TEA- and BTMA-MONT, respectively, after the dehydroxylation of the clay. Thermo-XRD analysis detected TEA-MONT tactoids with spacing 1.40 and 1.46 nm up to 300 °C. At 300 and 360 °C, LTSC-MONT tactoids were detected with spacing of 1.29 nm. At higher temperatures, HTSC-MONT-α and -β tactoids were detected with spacings of 1.28 and 1.13 nm, respectively. BTMA-MONT tactoids with spacings 1.46 and 1.53 nm were detected up to 250 °C. At 300 and 360 °C, LTSC-MONT tactoids were detected with a spacing of 1.38 nm. At higher temperatures, HTSC-MONT-α and -β tactoids were detected with spacings of 1.28 and 1.17 nm, respectively. At 650 °C, both clays were collapsed. HTSC-β-MONT differs from HTSC-α-MONT by having carbon atoms keying into the ditrigonal holes of the clay-O-planes. At 900 °C, the clay fraction is amorphous. Trace amounts of spinel and cristobalite are obtained from thermal recrystallization of amorphous meta-MONT. © 2012 Akadémiai Kiadó, Budapest, Hungary.