Development and gas permeation properties of microporous amorphous TiO2–ZrO2–organic composite membranes using chelating ligands

Sol–gel derived microporous amorphous TiO2–ZrO2–organic composite membranes were prepared by two different types of chelating ligands, diethanolamine (DEA) and isoeugenol (2-methoxy-4-propenylphenol, ISOH) as reaction inhibitors for hydrolysis and condensation of Ti- and Zr-alkoxide. The structural properties of the composite gels were characterized via a thermogravimetric study (TG), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and N2 adsorption analysis; and the optimized calcination atmosphere and temperature conditions for a microporous membrane were examined. A crack-free thin (50 nm) TiO2–ZrO2–organic layer for gas separation was formed on a SiO2–ZrO2 intermediate layer (150 nm) supported on a macroporous α-Al2O3 substrate as an asymmetric membrane. Compared with DEA, more of the ISOH and its remnants effectively remained after calcination, which promoted higher permeance and selectivity as a microporous gas separation membrane by forming bimodal microporous structures that narrowed the original TiO2–ZrO2 pores. A TiO2–ZrO2 membrane with ISOH calcined at 350 °C under a N2 atmosphere showed He and CO2 permeances of 1.0×10−6 and 2.0×10−7 mol m−2 s−1 Pa−1, respectively, at 200 °C. The CO2/N2 permeance ratio was 6.4 at 200 °C and 46 at 35 °C.