Gas Permeation Characteristics of TiO(2)-ZrO(2)-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(2)-ZrO(2)-aOCL composite sols via hydrolysis and polycondensation reactions with titanium(IV) isopropoxide (Ti(OC(3)H(7))(4)) and zirconium(IV) butoxide (Zr(OC(4)H(9))(4)). 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(2)-ZrO(2) composite material prepared using these two aOCLs showed an amorphous structure with no crystalline peaks for TiO(2) and ZrO(2). In N(2) adsorption/desorption measurements at 77 K, the TiO(2)-ZrO(2) samples using the aOCLs as a template appeared porous with a larger specific surface area than TiO(2)-ZrO(2) without aOCL. TiO(2)-ZrO(2)-aOCL composite membranes were prepared by coating and firing TiO(2)-ZrO(2)-aOCL sol onto a SiO(2) intermediate layer using an α-alumina porous tube as a substrate. Compared with the TiO(2)-ZrO(2) membrane, the TiO(2)-ZrO(2)-aOCL membranes had higher gas permselectivity. The TiO(2)-ZrO(2)-EF membrane showed a He permeance of 2.69 × 10(−6) mol m(−2) s(−1) Pa(−1) with permeance ratios of He/N(2) = 10.6 and He/CF(4) = 163, while the TiO(2)-ZrO(2)-MG membrane revealed a bit less He permeance at 8.56 × 10(−7) mol m(−2) s(−1) Pa(−1) with greater permeance ratios of He/N(2) = 61.7 and He/CF(4) = 209 at 200 °C. A microporous TiO(2)-ZrO(2) 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(2)-ZrO(2)-aOCL membranes.