Authors:R. Marinkovic-Neducin, E. Kiss, T. Cukic, and D. Obadovic
The purified bentonite parent clay, fraction ≤; 2 mm of montmorillonite type, has been pillared by various polyhydroxy cations,
Al, AlFe and AlCu, using conventional pillaring methods. The thermal behavior of PILCs was investigated by combination of
X-ray diffraction (XRD), thermal analysis (DTA, TG) and low temperature N2 adsorption/desorption (LTNA). Thermal stability
of Al-, AlFe- and AlCu-PILC samples was estimated after isothermal pretreatment in static air on the temperatures 300, 500,
600 and 900C. Crucial structural changes were not registered up to 600C, but the fine changes in interlayer surrounding
and porous/microporous structure being obvious at lower temperatures, depending on the nature of the second pillaring ion.
AlFe-PILC showed higher thermal stability of the texture, the AlCu-PILC having lower values and lower thermal stability concerning
both overall texture and micropore surface and volume. Poorer thermal stability of AlCu-PILC sample at higher temperatures
was confirmed, the presence of Cu in the system contributing to complete destruction of aluminum silicate structure, by 'extracting'
aluminum in stabile spinel form.
The swelling properties of Al-pillared clays, obtained from five different smectites, were studied using X-ray diffraction.
These clays, the dioctahedral beidellite and montmorillonite and the trioctahedral saponite, hectorite and laponite differ
in source of isomorphic substitution and represent a series of decreasing basicity along the siloxane plane. An Al oxyhydroxy
cation was inserted between the layers to form the respective pillared clays and these clays were heated incrementally to
600°C. The XRD peaks at each stage of heating were recorded as well as the same samples subsequently wetted. Basal spacings
of each clay at each stage of dehydration ↭d rehydration indicated that the swelling of tetrahedrally substituted saponite
and beidellite was indeed restricted, compared with the other three clays. This was attributed to greater basicity of the
oxygen plane of beidellite and saponite due to tetrahedral substitution of Si by Al, resulting in an increase in the strength
of hydrogen bonds between either water or the interlayer polyhydroxy cation and the clay.
The data from the XRD analyses helped in addition, to clarify the thermal transformations of the Keggin ion itself. According
to the changes in thed-spacings of the pillared clays it was concluded that the Keggin ion lost its structural water at ∼200°C and dehydroxylated
in a range beginning at 350°C. Between 500 to 600°C this polymer cation, which is thought to form the Al2O3 oxide, did not rehydrate.
Authors:Shmuel Yariv, Mikhail Borisover, and Isaak Lapides
, porosity of the clay particle, the clay layer charge, size, and shape of the adsorbed molecule and the presence of water [ 20 ].
In adsorptive clay, the ammonium cations play the role of pillars, similar to their role in Al-pillaredclay, holding