Effect of fluorine doping on the network pore structure of non-porous organosilica bis(triethoxysilyl)propane (BTESP) membranes for use in molecular separation

Long-chain organosilica bis(triethoxysilyl)propane (BTESP) membranes typically have a flexible non-porous structure. Fluorine was used to tune the network pore structure of BTESP membranes in an effort to improve the gas permeation properties. The network pore size was enlarged and the effect of calcination temperature on the network structure was evaluated based on gel and membrane characterizations. Fluorine-doped BTESP membranes calcined at 350 degrees C and 650 degrees C have shown H-2 permeance on the orders of 1.2 x 10(-6) mol m(-2) s(-1) Pa-1 and 1.5 x 10(-6) mol m(-2) s(-1) Pa-1 with H-2/N-2 selectivities of 8 and 6, respectively, which indicates similar pore sizes with lower condensation effect at high temperature of 650 degrees C, that was suppressed due to the presence of Si-F and C-F bonds. Undoped BTESP membranes, on the other hand, showed H-2/N-2 selectivity that was significantly lower-from 24 to 11 at 650 degrees C. FT-IR and N-2 adsorption isotherms clearly indicated that fluorine significantly decreased the Si-OH density and increased the surface area and micropore volume. Further water adsorption analysis revealed that fluorine significantly increased the hydrophobicity of the BTESP network structure. Overall, the results of this study endorse the effectiveness of fluorine to control the network pore structure in both wet and dry molecular separation systems.

Automated summary

By fluorine-doping, the network pore structure of BTESP membranes can be controlled to improve gas permeation properties and selectivity. Fluorine significantly reduced the Si-OH density, increased the surface area and micropore volume, and enhanced the hydrophobicity of the BTESP network structure.