Hydrothermal stability of fluorine‐induced microporous silica membranes: Effect of steam treatment conditions

A fluorine‐SiO 2 membrane was prepared using triethoxyfluorosilane (TEFS) as a Si precursor, and its hydrothermal stability was evaluated. The TEFS membrane calcined at 750°C had fewer Si‐OH and Si‐F groups in its network structure and showed H 2 permeance that was greater than 10 −6  mol m −2  s −1  Pa −1 with H 2 /N 2 and N 2 /SF 6 permeance ratios of 10 and 210, respectively. This membrane performance was relatively stable under the temperature (< 500°C) used for steam treatment, regardless of the steam partial pressure (30, 90 kPa). On the other hand, when the steam treatment temperature was increased beyond 500°C, gas permeance decreased significantly and the membrane became highly selective for He and H 2 over smaller molecules (He/N 2 : > 600, H 2 /N 2 : > 100). The relationship between the activation energy of H 2 and the permeance ratios (He/H 2 , He/H 2 O, H 2 /H 2 O) of a TEFS‐derived membrane under steam treatment higher than 600°C resulted in a network pore size that approximated in conventional microporous SiO 2 membranes.