Gas Permeation Characteristics of TiO₂-ZrO₂-Aromatic Organic Chelating Ligand (aOCL) Composite Membranes

• Published in: Membranes
• Main Authors: Takashi Tachibana, Tomohisa Yoshioka, Keizo Nakagawa, Takuji Shintani, Eiji Kamio, Hideto Matsuyama
• Format: Article
• Language: English
• Published: MDPI AG 2020-12-01
• Subjects: TiO₂-ZrO₂ composite membrane; aromatic organic chelating ligand; amorphous structure; micropore; gas permeation
• Online Access: https://www.mdpi.com/2077-0375/10/12/388

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 TiO₂-ZrO₂-aOCL composite sols via hydrolysis and polycondensation reactions with titanium(IV) isopropoxide (Ti(OC₃H₇)₄) and zirconium(IV) butoxide (Zr(OC₄H₉)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 TiO₂-ZrO₂ composite material prepared using these two aOCLs showed an amorphous structure with no crystalline peaks for TiO₂ and ZrO₂. In N₂ adsorption/desorption measurements at 77 K, the TiO₂-ZrO₂ samples using the aOCLs as a template appeared porous with a larger specific surface area than TiO₂-ZrO₂ without aOCL. TiO₂-ZrO₂-aOCL composite membranes were prepared by coating and firing TiO₂-ZrO₂-aOCL sol onto a SiO₂ intermediate layer using an α-alumina porous tube as a substrate. Compared with the TiO₂-ZrO₂ membrane, the TiO₂-ZrO₂-aOCL membranes had higher gas permselectivity. The TiO₂-ZrO₂-EF membrane showed a He permeance of 2.69 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ with permeance ratios of He/N₂ = 10.6 and He/CF₄ = 163, while the TiO₂-ZrO₂-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/N₂ = 61.7 and He/CF₄ = 209 at 200 °C. A microporous TiO₂-ZrO₂ 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 TiO₂-ZrO₂-aOCL membranes.