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

Abstract

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 N 2 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 CO 2 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.