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

[Image: see text] 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.