Development of Reaction/Separation Devices for Microfabricated Chemical Systems by Ice-Templating

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Microfabricated chemical systems (MCSs) have been greatly interested in recent years. The unthors have proposed the ice-template method, which uses micrometer-sized ice crystals as a template, to prepare porous materials with various morphologies such as microbiber and microhoneycomb. In the present work the reaction/separation devices for MCSs were developed by using this method.Silica gel microhoneycombs (SMHs) were prepared through the ice-template method. Ice crystals used as a template, which had a continuous rod shape, a polygonal cross section and ordered diameters, were grown inside precursor silica hydrogels under a condition where the pseudo-steady-state growth of them continues. Besides their ordered macroporosity, micro-/mesopores develop inside the honeycomb walls through the freeze-drying of SMHs soaked in tert-butyl alcohol. SMHs had straight and polygonal macroporous voids, which are created and retained through the formation and removal of the ice crystals. Micromorpho … More logy including macropore size and wall thickness, micro-/mesoporosity inside the honeycomb walls, and thermal stability of SMHs were investigated in detail through scanning electron microscopy observation, nitrogen adsorptiondesorption measurements, and thermogravimetric analysis. It was found that the macropore size of the SMHs can be controlled by changing the immersion rate into a cold bath and the freezing temperature without changing the micro-/mesoporosity of their honeycomb walls. It was also found that the thickness of the honeycomb walls was affected by the SiO_2 concentration and the macropore size. On the other hand, the porosity of the honeycomb walls could be controlled to be microporous as well as mesoporous by hydrothermal treatment of as-prepared SMHs in basic aqueous solutions. Moreover, it was found that SMHs with developed mesopores showed a higher stability against heat treatment. SMHs were successfully fabricated as separation columns of 1/16 to 1/2 inch for high performance liquid chromatography (HPLC), and the columns prepared showed small pressure drop when they were applied to HPLC.SiO_2-Al_2O_3 cryogel microhoneycobs, which had bronsted acid cites and catalytic activities, were prepared by ice-templating. Al atoms were incorporated into silica frameworks at a nanometer level. TiO_2-SiO_2 cryogel microhoneycombs were also successfully prepared. It was found that TiO_2 existed as extremely fine particles by using a transition electron microscope. The microhoneycombs showed higher photocatalytic activities for decomposition of large-organic molecules than a commercial photocatalyst. Less