Structural Design of Periodic Mesoporous Organosilica by Micelle Packing Control Using Gemini Surfactants

摘要

Ordered mesoporous materials have attracted a lot of interests due to their high surface areas and large pore sizes in the range of 2 nm and 10 nm. In 1999, a new type of mesoporous materials containing bridging organic groups within the framework, named periodic mesoporous organosilica (PMO) materials, was reported. The organic groups which are dispersed in molecular scale within the framework gives intense potentials for catalytic applications due to the hydrothermal stability and hydrophobic property. It is well known that the nature of templating materials such as size, charge and shape is one of the most important factors for the design and synthesis of mesoporous materials. Especially, the effective surfactant packing parameter is an essential molecular structure-directing index to design the mesostructured products and it can be defined as g = V/ a_0 l (V = total molecular volume, a_0 = effective surface head group area, l = kinetic surfactant tail length). In the present work, Gemini-type surfactants, whose g value can be controlled easily compared to normal surfactants, are adopted as the structure directing agent for the synthesis of PMO materials. The Gemini surfactants have the general formula of C_nH_(2n+1)N~+(CH_3)_2(CH_2)_3N~+(CH_3))_2C_nH_(2n+1) (designated as C_(n-s-n)). Several mesostructured PMO materials are synthesized by optimizing the micelle packing parameter and synthetic condition.