On the mechanical stability of mesoporous silica SBA-15

Mesoporous silica SBA-15 was synthesised at 80 °C. The calcined solids were exposed to a unilateral external pressure in the range 16–191 MPa in order to monitor the impact of the mechanical pressure on the properties of SBA-15. N2 adsorption–desorption measurements, XRD and UV-Raman spectroscopy was used in order to evaluate the changes occurring in the SBA-15. For the XRD measurement, an internal Si standard was used to correct the position of the SBA-15 patterns. It appeared that the elevated pressure has no influence on the hexagonal cell parameter a. Through the N2 sorption measurements the fraction of the preserved mesoporous structure was estimated to be 60% when the highest pressure has been used. As the remaining part of the material is irreversibly disintegrated into small particles, the pressed sample is considered to be heterogeneous. However, the preserved fraction is slightly modified, showing a smaller pore width and plugs located within the mesopores. The plugs most likely originate from a disintegrated fraction of the SBA-15. UV-Raman spectroscopy shows that the relative intensity of the band associated with the siliceous network (ω1) has decreased on the pressed samples resulting in a less ordered material possessing an enhanced population of silanols as compared to parent SBA-15. We propose that the disorder introduced by pressing is responsible for the observed expansion of the SBA-15 walls, which is detected for the samples treated at higher pressures (112, 191 MPa).