Fabrication of mixed matrix membranes with zinc ion loaded titanium dioxide for improved CO₂ separation

To date, mixed matrix membranes with nano-filler was considered to be an effective method to enhance the gas permselectivity of membrane separation. In this work, mixed matrix membranes for the facilitated transport of CO₂ were prepared. Hexafluoroisopropylidene diphthalic anhydride - based aromatic polyimide was applied as polymeric matrix, while the zinc ion functionalized titanium dioxide spherical nano-particle was selected as nano-filler. The physical property, chemical structure and membranes morphology were characterized by FT-IR, TG, XRD, SEM, CA and XPS. Gas permselectivity was investigated using binary mixture gas of CO₂/N₂ and CO₂/CH₄, respectively. The effects of nano-filler content, functional group, operation temperature on gas permselectivity were studied. Results show that the incorporation of spherical nano-filler can effectively restrict the polymer chain packing and lead to low crystallinity. By incorporation of zinc ion modified spherical nano-filler, the CO₂ permeability increased about 68.7~78.7%. PI-TiO₂-PDA-Zn²⁺ mixed matrix membranes with 7.5 wt% nano-filler addition displayed the highest CO₂ permeability (145.37 Barrer for CO₂/N₂ feed gas and 108.36 Barrer for CO₂/CH₄ feed gas, 1 Barrer = 7.5 × 10^-18 m² s⁻¹ Pa⁻¹) and satisfied CO₂/inert gas selectivity (CO₂/N₂ selectivity of 49.28 and CO₂/ CH₄ selectivity of 49.48). CO₂ permeability increased and selectivity decreased with the elevated temperature. Besides, the membrane exhibited good stability in the 30 days testing.