Thermal Stability of Periodic Mesoporous SiCO Glasses

Periodic Mesoporous Organosilicas (PMOs) with 2D-hexagonal and cubic Pm3n structures have been prepared from bis(trialkoxysilyl)ethane and cetyltrimethylammonium chloride. The two samples have been pyrolyzed under argon up to 1000 °C. Study by X-ray diffraction (synchrotron radiation) allows the thermal stability of both structures to be followed as a function of the pyrolysis temperature. While the 2D-hexagonal structure collapses after pyrolysis at 800 °C, the cubic Pm3n structure is retained up to 1000 °C. Further characterizations were performed by ²⁹Si MAS-NMR, N₂ adsorption-desorption experiments and elemental analysis. At 1000 °C, the first sample can be described as a mixture of silica and a free C phase, while the cubic one is a true SiCO glass with mixed SiC_xO_{4 – x} units (x = 0,1,2) and a very large surface area of 730 m²/g.