Sol-gel derived microporous amorphous TiO2-ZrO2-organic composite membranes were prepared by two different types of chelating ligands, cliethanolamine (DEA) and isoeugenol (2-merhoxy-4-propenyl-phenol, 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 N-2 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 alpha-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 rnicroporous gas separation membrane by forming bimodal microporous structures that narrowed the original TiO2-ZrO2 pores. A TiO2-ZrO2 membrane with [SOH calcined at 350 degrees C under a N-2 atmosphere showed He and CO2 permeances of 1.0 x 10(-6) and 2.0 x 10(-7) mol m(-2) s(-1) Pa-1, respectively, at 200 C. The CO2/N-2 permeance ratio was 64 at 200 degrees C and 46 at 35 degrees C. (c) 2014 Elsevier B.V. All rights reserved.