Understanding the hydrothermal stability of large-pore periodic mesoporous organosilicas and pure silicas

The hydrothermal stability of mesoporous materials is a crucial parameter in practical applications. In this study, well-ordered 2D hexagonal (p6mm) mesoporous organosilica and silica materials with a SBA-15 structure (PMO-SBA-15 and SBA-15) and 3D cubic (Im3m) mesoporous organosilica and silica materials (PMO-SBA-16 and SBA-16) were prepared in strongly acidic media in the presence of inorganic salts using triblock copolymers P123 and F127 as the templates, respectively. The hydrothermal stability of the materials in boiling water was investigated by means of small-angle X-ray scattering (SAXS), nitrogen adsorption, transmission electron microscope (TEM), scanning electron microscope (SEM), and 29Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR). It was observed that both PMO-SBA-15 and PMO-SBA-16 exhibited an unprecedented hydrothermal stability for as long as 60 days without any loss of structural integrity. In sharp contrast, a significant degradation of structural ordering of mesoporous SBA-15 and SBA-16 silicas was observed when subjected to boiling water for only 10 days. The reasons causing such a remarkable difference in terms of hydrothermal stability between PMO materials and mesoporous silicas were discussed.