SPEEK/amine-functionalized TiO2 submicrospheres mixed matrix membranes for CO2 separation

Mixed matrix membranes (MMMs) composed of sulfonated poly(ether ether ketone) (SPEEK) and amine-functionalized titania submicrospheres were prepared. TiO2 submicrospheres (~300 nm) were amine-functionalized through a facile two-step method by using dopamine (DA) and polyethyleneimine (PEI) in succession. The resultant TiO2–DA–PEI microspheres were incorporated into SPEEK with a sulfonation degree of 67%. Grafting PEI with abundant amine groups onto the titania fillers remarkably increased the content of facilitated transport sites in the membranes, leading to an increment in both gas permeability and selectivity. High humidity also contributed to the facilitated transport of CO2 via the generation of HCO3−. The highest ideal selectivities of the SPEEK/TiO2–DA–PEI membranes for CO2/CH4 and CO2/N2 were 58 and 64, respectively, with a CO2 permeability of 1629 Barrer. Besides, the mechanical and thermal stabilities of the membranes were also enhanced compared to pure SPEEK membrane.