Tailoring a Thermally Stable Amorphous SiOC Structure for the Separation of Large Molecules: The Effect of Calcination Temperature on SiOC Structures and Gas Permeation Properties

摘要

A SiOC membrane with high oxidative stability for gas separation was tailored by utilizing vinyltrimethoxysilane, triethoxysilane, and 1,1,3,3-tetramethyldisiloxane as Si precursors. Amorphous SiOC networks were formed via the condensation of Si–OH groups, the hydrosilylation of Si–H and Si–CH═CH_(2) groups, and a crosslinking reaction of Si–CH_(3) groups, respectively. The crosslinking of Si–CH_(3) groups at temperatures ranging from 600 to 700 °C under a N_(2) atmosphere was quite effective in constructing a Si–CH_(2)–Si unit without the formation of mesopores, which was confirmed by the results of N_(2) adsorption and by the gas permeation properties. The network pore size of the SiOC membrane calcined at 700 °C under N_(2) showed high oxidative stability at 500 °C and was appropriate for the separation of large molecules (H_(2)/CF_(4) selectivity: 640, H_(2)/SF_(6): 2900, N_(2)/CF_(4): 98). A SiOC membrane calcined at 800 °C showed H_(2)/N_(2) selectivity of 62, which was approximately 10 times higher than that calcined at 700 °C because the SiOC networks were densified by the cleavage and redistribution reactions of Si–C and Si–O groups.