A Thermal Study of Porous Si-pillared Montmorillonite with High Surface Area

Depending on the fact that most pillared clays show poor thermal stability, the study on the synthesis of novel Si-pillared montmorillonites (Si-MMT) with high thermal stability have been carried out. Furthermore, powder X-ray diffraction (XRD), Fourier transformation infra-red spectra (FTIR), nitrogen adsorption-desorption isotherms were applied in order to study the thermal stability and mechanisms of the pillared materials. A mechanism corresponding to Si-MMT with a good thermal stability was thus established: after calcination, protons are liberated by dehydration or dehydroxylation. These protons disrupt the silicon-oxygen-aluminium bridges where there are Al substitutions in the tetrahedral sheet of the montmorillonite. Some of silicon and aluminum tetrahedra invert to react with the pillaring agents and yield covalent bonds which firmly fix the pillars to the host clay. The Si-MMT are thermally stable up to 800degC and possess large basal spacings of about 2.5 nm after thermal treatment at 800degC.