Microporous niobia–silica membranes: Influence of sol composition and structure on gas transport properties

Preparation of particulate/polymeric sol–gel derived microporous silica membranes and determination of their gas permeation properties

“…The literature values [6,13,14,[28][29][30][31][32] given in Fig. 20 indicate either positive activation energies for CO 2 permeance or negative values as well as the non-activated permeance as those in the study of Uhlhorn et al [29].…”

“…CO 2 transport but also has found as activated with activation energy of 10 kJ/mol by changing synthesis condition [29]. The largest negative value was reported by Boffa et al [6], for niobia-silica membranes with the lowest permeance values because of strong interaction between CO 2 and the pore wall. The value calculated for sp5-5 nm silica membranes is comparable with those reported in the literature.…”

“…The activation energy for permeation (combination of heat of sorption and activation energy for micropore diffusion) can be obtained by the following modified Fick's law equation [6,13,14,25,26]:…”

“…The design/stabilization of silica membrane pore structures by the incorporation of transition metals has been recently studied in order to improve the hydro/thermal stability of the membranes [6][7][8][9][10][11]. Research on this subject is still in progress and it is stated that the enhanced hydrothermal stability may be due to the reduced motion of silanol groups through the formation of more stable bonds and a denser pore structure with transition metal addition.…”

“…Research on this subject is still in progress and it is stated that the enhanced hydrothermal stability may be due to the reduced motion of silanol groups through the formation of more stable bonds and a denser pore structure with transition metal addition. Boffa et al [6] stated that the consolidation/packing behaviour of silica network was modified by introducing Nb 5+ ions and the niobia-silica mixed oxide membrane became denser due to the increasing coordination between Nb 5+ and oxygen ions in the polymeric silica network. The close relationship between the niobia-silica sol structure and the final membrane pore structure/microstructure was established by the DLS characterizations during sol species growth/structural development and was further shown by their He and H 2 permeation differences.…”