In Chemeca 2007, we had discussed on the formation mechanism of mesoporous silica microsphere (MSM) in the presence of dodecyl amine as template and catalysis. In this study, we will further discuss on this issue, but it is focused on the effects of alkyl-chain-length of primary amine on the characteristics of MSM.
We prepared MSM by the mixing of tetraethoxysilane (TEOS) and dodecylamine (DDA) or tetradecylamine (TDA) in 60 vol % ethanol solutions. The effects of ammonia concentration in the reaction media on the characteristics, such as diameter, specific surface area and pore volume, of MSM were obtained.
In presence of DDA, the diameter and the BET specific surface area of MSM were decreased with the increase in ammonia concentration. It was found from the measurement of the residue DDA concentration by the use of HPLC that the DDA could not be trapped into MSM at higher ammonia concentration above 0.7 M. The phenomena were caused by the hindering of the interaction between TEOS and DDA due to be the presence of ammonium ion.
On the other hand, in the presence of TDA, the diameter of MSM slowly decreased with ammonia concentration, but the BET specific surface area and pore volume were increased with ammonia concentration. This conflicting result may be caused by the easy formation and/or the shape of molecular assembly due to the difference alkyl-chain-length of primary amine. We will discuss in detail on this issue.