Microemulsion templating of siliceous mesostructured cellular foams with well-defined ultralarge mesopores

Siliceous mesostructured cellular foams (MCFs) with well-defined ultralarge mesopores and hydrothermally robust frameworks are described. The MCFs are templated by oil-in-water microemulsions and are characterized by small-an gle X-ray scattering, nitrogen sorption, transmission electron microscopy, scanning electron microscopy, thermogravimetry, and differential thermal an alysis. The MCFs consist of uniform spherical cells measuring 24-42 nm in d iameter, possess BET surface areas up to 1000 m(2)/g and porosities of 80-8 4%, and give, because of their pores with small size distributions, higher- order scattering peaks even in the absence of long-range order. Windows wit h diameters of 9-22 nm and narrow size distribution interconnect the cells. The pore size can be controlled by adjusting the amount of the organic swe lling agent that is added and by varying the aging temperature. Adding ammo nium fluoride selectively enlarges the windows by 50-80%. In addition, the windows can be enlarged by postsynthesis treatment in hot water. The MCF ma terials resemble aerogels, but offer the benefits of a facilitated synthesi s in combination with well-defined pore and wall structure, thick walls, an d high hydrothermal stability. The open system of large pores give MCFs uni que advantages as catalyst supports and separation media for processes invo lving large molecules, and the high porosities make them of interest; for e lectrical and thermal insulation applications.