Effect of post-synthesis treatment on the stability and surface properties of MCM-48 silica

The effect of post-synthesis hydrothermal treatments on MCM-48 has been studied by 29Si MAS-NMR and IR spectroscopies, X-ray diffraction, thermal gravimetry, and gas volumetry. Special attention has been given to the characterisation of the precursors before calcination and a method to evaluate the pore opening of MCM-48 from diffraction and volumetric data is given. The hydrothermal treatment does not affect the organisation of the cetyltrimethylammonium mesophase but extracts a fraction of the surfactant and increases the thickness of the silica wall. The lower area of the silica-surfactant interface after hydrothermal treatment brings about an improved stability of MCM-48 during calcination and allows the pore size of the precursor to be preserved in the calcined solid. After calcination, the hydrothermally treated samples are less prone to rehydrate and, as a consequence, their stability upon storage in moist atmosphere is dramatically improved.