Influence of water on the pillaring of montmorillonite with aminopropyltriethoxysilane

Silica pillaring of montmorillonite has been carried out using aminopropyltriethoxysilane (APTS) as pillaring precursor. Several synthesis parameters, i.e. reaction temperature, reaction time, concentration of components, etc., are of importance in this synthesis. However, the concentrations of APTS and H2O under which the hydrolysis is performed have a paramount effect on the molecular structure and the degree of polymerization of the pillaring precursors, and therefore, also on the porosity of the obtained silica intercalated clay. X-ray diffraction (XRD) analysis and diffuse reflectance infrared Fourier transform (DRIFT) spectra reveal that the presence of water in the system is one of the most important parameters in the reaction sequence. These results are refined and confirmed by transmission electron microscopy (TEM). Combining the results of all the applied techniques, two types of APTS interaction with the clay can be observed: internal and external adsorption depending on the conditions used. Besides the influence of the water concentration, the influence of the use of templating ions (cetyltrimethylammonium) on the synthesis is also studied. In the case of the templated approach, in which the alkylammonium ions are pre-adsorbed on the clay prior to the pillaring with APTS, a surface area and a pore volume as high as 487 g-1 and 0.45 cm3 g-1 have been obtained.