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

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. CH2 groups, and a crosslinking reaction of Si-CH3 groups, respectively. The crosslinking of Si-CH3 groups at temperatures ranging from 600 to 700 degrees C under a N-2 atmosphere was quite effective in constructing a Si-CH2-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 degrees C under N-2 showed high oxidative stability at 500 degrees C and was appropriate for the separation of large molecules (H-2/CF4 selectivity: 640, H-2/SF6: 2900, N-2/CF4: 98). A SiOC membrane calcined at 800 degrees C showed H-2/N-2 selectivity of 62, which was approximately 10 times higher than that calcined at 700 degrees C because the SiOC networks were densified by the cleavage and redistribution reactions of Si-C and Si-O groups.