Journal of Siberian Federal University. Chemistry / Hydrothermal Stability of Mesostructured Silicate MCM-41 in Connection with Pathways Synthesis

Full text (.pdf)
Issue
Journal of Siberian Federal University. Chemistry. 2011 4 (1)
Authors
Kirik, Sergei D.; Parfenov, Vladimir A.
Contact information
Kirik, Sergei D. : Institute of Chemistry and Chemical Technology SB RAS Siberian Federal University , 42 K.Marx st., Krasnoyarsk, 660049 Russia 79 Svobodny, Krasnoyarsk, 660041 Russia , e-mail: ; Parfenov, Vladimir A. : Institute of Chemistry and Chemical Technology SB RAS , 42 K.Marx st., Krasnoyarsk, 660049 Russia
Keywords
mesostructured mesoporous materials; template synthesis; hydrothermal stability; X-powder diffraction; continuous electron density approach
Abstract

The changes of the MCM-41 silicate material mesostructure during the main synthesis stages depending on the modified conditions have been investigated. To estimate the parameters of the mesostructured state the X-ray powder diffraction has been applied in combination with the continuous electron density approach. The X-ray data are supplemented by adsorption measurements. Consideration has been given to the variations of the synthesis conditions affecting the hydrothermal stability, in particular the creation of the basicity of the synthesis solution using ammonia and alkali and the substitution of the synthesis solution with water and a salt solution at hydrothermal treatment. It has been shown that polycondensation of the silicate in closely-packed cylindrical organosilicate micelles occurs under the conditions of chemical and steric factors. The polycondensation process is anisotropic and results in numerous pathways of the final solid product formation, showing the variety of mesostructured forms. It has been established that increasing the pore diameter, as a rule, is due to the osmotic pressure of water. Moreover, if the silica polycondensation is slowed down or sterically difficult, the pores acquire the hexagonal shape, and under the conditions favourable for the polycondensation, they are cylindrical. The pore wall is a two-layer molecular pack of silica 0.8-1.0 nm in thickness. The wall growth using tetraethoxysilan ends by the pore healing with silica and the loss of the specific inner volume and surface. The material treatment by a sodium silicate solution results in the effect of the surface «healing» and increased hydrothermal stability. Using ammonia as the medium basicity factor provides the highest rate of the silica polycondensation and high hydrothermal stability of the product.

Pages
50-72
Paper at repository of SibFU
https://elib.sfu-kras.ru/handle/2311/2407