| Abstract
| - New opportunities are discussed for the pore-size engineering of mesoporous silicas using amines as swellingagents. It was shown that N,N-dimethylhexadecylamine (DMHA) is a convenient expander allowing for thesynthesis of large-pore MCM-41 in mild conditions. Their pore size increased and the structural orderingdecreased as the amount of the amine in the synthesis gel increased. The material with the largest pore sizeattained (7.7 nm) exhibited narrow pore-size distribution, very large primary mesopore volume, but a disorderedpore system. Other amines, such as trioctylamine and tridodecylamine, were also found to be suitable forpreparation of large-pore MCM-41 but not as efficient as DMHA. Addition of dimethyldecylamine (DMDA),dimethyloctylamine (DMOA), and small trialkylamines to the synthesis gel did not lead to the pore sizeenlargement but decreased the structural uniformity and in some cases resulted in development of microporosity.It was also demonstrated that it is possible to induce up to 3-fold enlargement of pore size of as-synthesizedMCM-41 by treating it in an aqueous emulsion of an appropriate amine, such as DMHA, DMDA, and DMOA.This novel synthesis approach allowed us to prepare materials with pore sizes up to 11 nm, pore volumes upto 2.4 cm3/g, large surface areas (about 1000 m2/g), and narrow pore-size distributions. Although it waspossible to achieve a limited pore-size increase (ca. 20%) with retention of the hexagonal structure, moresignificant enlargement was accompanied by loss of ordering. Structural features of materials restructuredunder different conditions, such as temperature, treatment time, and nature of the amine used, are described,and structural changes during the pore size enlargement are discussed.
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