Thermal-Degradation Process Analysis of Mesoporous Silica in Different Atmospheres

摘要

The thermal-degradation process of the mesoporous structure in silica MCM-41 was investigated in the present research via a series of thermal-stability experiments in different atmospheres with varied technique analysis(N_2-sorp-tion,XRD,IR,and NMR spectra).The research showed that the atmosphere was also a very important factor to affect the thermal stability of mesoporous silica as well as the temperature and time;the oxygen atmosphere obviously accelerated the degradation process of the ordered pore structure in mesoporous silica.We considered that the thermal vibration of atom groups,silanol condensation,and the reconstruction of bridge oxygen bonds between SiO_4 tetrahedra in the mesopore wall can be the main causes resulting in the contraction of the inorganic networks and the degradation of the pore structure in mesoporous silica.The oxygen molecule could play an important role during the heat treatment.The oxygen can not only promote silanol condensation,but also make some original bridge oxygen bonds rupture more easily,and then the ruptured units immediately reconstruct more stable bonds with other ruptured units,SiO_4,which results in the contraction of inorganic networks and degradation of the mesoporous structure.