Formation Mechanism of Mesoporous Silica Microsphere in the Presence of Dodecylamine as Template and Catalysis
The Stober method is well-known to prepare the spherical silica particles, that the tetraethoxysilane are hydrolyzed and condensed in mixed solvent of ethanol and water by using ammonia as a catalyst. Some methods to prepare the mesoporous silica microsphere (MSM) have been reported as analogy of this Stober method. The methods can be classified into two systems; MSM were prepared (1) from TEOS in the presence of a quaternary ammonium salt and ammonia, and (2) from TEOS in the presence of a primary alkylamine without ammonia. The diameter of MSM prepared by these reaction systems was ranged from sub-micrometer to 1.5 micrometer. The specific surface area was more than 1,000 m2/g. The pore diameter was several nanometers, which was about twice of surfactant length. However, there are few reports on the formation mechanism of the MSM.
In this study, the MSM was prepared under the presence of dodecylamine and ammonia in mixed solvent of ethanol and water. The diameter and the specific surface area of MSM were decreased with the increase in ammonia concentration under the constant TEOS and dodecylamine concentrations. The formation processes in this system were inverstigaed by a dynamic light scattering (DLS) method. We will discuss the formation mechanism of MSM in this reaction system. This method can be applied to preparation the functionalized MSM from the co-condensation of TEOS and silicon alkoxide with some functional groups. We parepared MSM fuctionalized with the thiol- and aminopropyl- groups and studied the adsorption properties for the functionalized MSM.