Ice Templating for Silica Gels

The macropore size can be tuned in the range 4—40 pm since the diameter of the ice crystals depends on the immersion velocity u and the temperature difference (To - Too) as 

The wall thickness can be adjusted from 0.2 to 2 pm it is proportional to the product of the ice crystal diameter dice and the silica concentration in the starter solution. The overall porosity of the micro-honeycomb is about 94% that of the walls around 40% (corresponding to a random packing of monosized spheres). Meso- and micro-porosity can be adjusted independently through hydrothermal treatment the initial high BET surface area (up to 900m g ) decreases and the small pores (radii 1 nm) grow (up to 45 nm) so that mesopore volume is created. Microhoneycombs are suitable for many applications, since the macrochannels ensure alow pressure drop, and diffusion parameters in the porous walls can be engineered. 

A modern use of titania-silica microhoneycombs may be in self cleaning applications (Tamon et al, 2006b) by the sol-gel process, the titania particles are more finely dispersed in the matrix than by conventional methods, and much higher BET surface areas can be reached consequently, pulverized gels proved to have outstanding photocatalytic activity in the decomposition of large organic molecules. 

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