Silicon-titanium oxycarbide glasses as bimodal porous inorganic membranes

Porous oxycarbide Si-Ti-O-C glasses have been studied as potential materials for inorganic membranes. Such materials were prepared by pyrolysis of hybrid materials in nitrogen atmosphere. These hybrids were synthesized by the sol-gel process using tetraethylortosilicate (TEOS), polydimethylsiloxane (PDMS) and titanium orthotitanate (TBOT) as raw material. The influence of the TEOS/TBOT molar ratio on the pore size distribution has been studied in the range of pyrolysis temperatures between 400 and 1100 °C. The oxycarbide materials were characterized by FT-IR and NMR spectroscopies, XRD, mercury porosimetry, nitrogen adsorption and SEM. Bimodal pore size distributions showed one mode close to 0.02 μm and the other one in the range between 1 and 100 μm of pore diameter. Such pore sizes increase with the amount of TBOT. Reduced effective diffusivities were calculated by a theoretical model taking into account the mentioned pore size distributions. Diffusivities appeared in the range from 0.46 to 0.77 and increase with the titanium concentration in the oxycarbide.