Gas Permeation Characteristics of TiO-ZrO-Aromatic Organic Chelating Ligand (aOCL) Composite Membranes.

Methyl gallate (MG) and ethyl ferulate (EF) with a benzene ring were separately used as aromatic organic chelating ligands (aOCLs) to prepare two versions of TiO-ZrO-aOCL composite sols via hydrolysis and polycondensation reactions with titanium(IV) isopropoxide (Ti(OCH)) and zirconium(IV) butoxide (Zr(OCH)). Thermogravimetric and FT-IR analysis of dry gels revealed that aromatic rings were present in the residual organic matter when the gel was fired under nitrogen at 300 °C. In X-ray diffraction (XRD) measurements, the TiO-ZrO composite material prepared using these two aOCLs showed an amorphous structure with no crystalline peaks for TiO and ZrO. In N adsorption/desorption measurements at 77 K, the TiO-ZrO samples using the aOCLs as a template appeared porous with a larger specific surface area than TiO-ZrO without aOCL. TiO-ZrO-aOCL composite membranes were prepared by coating and firing TiO-ZrO-aOCL sol onto a SiO intermediate layer using an α-alumina porous tube as a substrate. Compared with the TiO-ZrO membrane, the TiO-ZrO-aOCL membranes had higher gas permselectivity. The TiO-ZrO-EF membrane showed a He permeance of 2.69 × 10 mol m s Pa with permeance ratios of He/N = 10.6 and He/CF = 163, while the TiO-ZrO-MG membrane revealed a bit less He permeance at 8.56 × 10 mol m s Pa with greater permeance ratios of He/N = 61.7 and He/CF = 209 at 200 °C. A microporous TiO-ZrO amorphous structure was obtained by introducing aOCL. The differences in the side chains of each aOCL could possibly account for the differences in the microporous structures of the resultant TiO-ZrO-aOCL membranes.