Silica-organic hybrid membranes were successfully prepared on -alumina substrates by using a counter diffusion CVD method. Propyltrimethoxysilane (PrTMOS) was employed as a silica source, and O 3 was used as a reactant. Deposition temperatures of the CVD were very important parameters for the membrane properties. C 3 H 6 /C 3 H 8 peremeance ratio was 12.1 at 320 through a membrane prepared at 320 . C 3 H 6 /C 3 H 8 peremeance ratios were proportional to N 2 /SF 6 permeance ratios showing that the C 3 H 6 /C 3 H 8 selectivity are due to a molecular sieving mechanism. The decomposition mechanism of propyl groups on silica surface was discussed by using powders prepared by hydrolysis of PrTMOS. Propyl groups were partially decomposed under 320 of an O 3 atmosphere. This indicates that the obtained membrane was a silica-organic hybrid membrane.

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H 2 permselective silica hybrid membranes were successfully prepared by using a novel deposition method. H 2 /SF 6 permeances ratio was over 3000 through the membrane prepared by a PrTMOS/O 3 counter diffusion CVD method at 270°C. H 2 permeance through this membrane was 9.1 x 10 7 mol m 2 s 1 Pa 1 that is two orders higher than that through a silica membrane prepared by a TMOS/O 2 counter diffusion CVD method at 600 °C. A high H 2 permeance membrane was obtained from high O 3 concentration during the deposition. Effects of deposition temperatures were investigated. Deposition temperature was important parameter to control pore size of the membrane. H 2 permselctive membrane was obtained at 240°C deposition, while N 2 permselective membrane was obtained at 270°C deposition. Pore size of the membranes increased with increasing the deposition temperatures upto270°C.C 3 H 6 /C 3 H 8 gas separation and C 6 H 6 /C 6 H 12 pervaporation separation were investigated using PrTMOS membranes by changing deposition conditions. The maximum C 3 H 6 /C 3 H 8 permeance ratio was 12.1 at the 320 °C permeation test. On the other hand, the maximum C 6 H 6 /C 6 H 12 separation factor was 113 at the 320 °C deposition by changing O 3 flow rate. All the selectivities were considered to be a molecular sieving mechanism. Many types of the membranes were obtained by controlling the pore sizes of the membranes.