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.