Pore size control of mesoporous molecular sieves using different organic auxiliary chemicals

Mesoporous silica molecular sieves: MCM-41 and SBA-15 with various pore sizes were synthesized using four different types of organic auxiliary chemicals-methyl-substituted benzene (1,3,5-, 1,2,4- or 1,2,3-trimethylbenzene), isopropyl-substituted benzene (1-, 1,3-di- or 1,3,5-tri-isopropylbenzene), alkane (octane, nonane, decane, tridecane, hexadecane or eicosane) and 1-octanol under hydrothermal conditions. Resultant materials have been characterized for their structural regularity by X-ray diffraction and nitrogen adsorption studies. Mesoporous materials with enlarged pore diameter can be obtained using methyl-substituted benzene, isopropyl-substituted benzene or alkane as organic auxiliary chemical and the degree of their influence on the pore size is in the following order: alkane < isopropyl-substituted benzene < methyl-substituted benzene. It is difficult to prepare MCM-41 and SBA-15 with mesoporous structures using 1-octanol under the present synthesis process. Depending on the type and amount of auxiliary chemical, the BJH pore diameter of MCM-41 can be controlled up to 9.1 nm and that of SBA-15 up to 43.0 nm; however, the X-ray diffraction, BJH pore size distribution and sharpness of BJH pores of the resulting mesoporous materials changed markedly. A plausible mesoporous phase formation mechanism in the presence of different organic auxiliary chemicals has been suggested. (C) 2003 Elsevier Inc. All rights reserved.