Calcination and thermal degradation mechanisms of triblock copolymer template in SBA-15 materials

The calcination under air and degradation under inert atmosphere of as made SBA-15 surfactant templated mesostructured silica materials were studied using a combination of N₂ sorption at −196 °C, mass spectrometry (MS) monitored temperature programmed oxidation and degradation, thermogravimetric analysis (TGA), ¹³C MAS NMR and Fourier transform infrared (FTIR) spectroscopy. The characterization of the materials treated at different temperatures under oxidative and inert atmospheres indicated that both processes follow stepwise mechanisms. SBA-15 materials exhibit three families of pores: primary main mesopores, complementary intrawall mesopores (>2 nm) and intrawall micropores (<2 nm). Under oxidative atmosphere, the primary mesopores and the larger framework intrawall pores are first emptied below 200 °C with the production of volatile organic compounds (VOCs). This step is followed by an oxidation of the PEO chains from the intrawall micropores (<2 nm) producing CO₂ by combustion. Under inert atmosphere, the degradation of the organic template also begins first in the primary mesopores. However, an increase in the pore diameter up to 550 °C indicates that the complete liberation of primary mesopores is much slower than for calcination under air and occurs simultaneously with the removal of the PEO chains occluded within framework micropores.