Effects of iron catalyst on gas transport properties of ion-irradiated asymmetric polyimide membranes

In this study, we focused on the effects of the carbon structures on the gas permeability and selectivity of the asymmetric polyimide membranes prepared by He+-irradiation using iron (III) acetylacetonate (AAI) as the catalyst. The irradiated asymmetric membranes consisted of a defect-free carbonized ultrathin skin layer and indicated a molecular sieving-like effect due to the surface carbonization similar to carbon molecular membranes. The Raman spectrum of the irradiated membranes included two well-known D (1360 cm−1) and G (1580 cm−1) peaks and two additional new peaks around 1150 and 1500 cm−1. Interestingly, the graphitic and amorphous structures at 1580 and 1500 cm−1 in the membranes increased with an increase in the AAI content. Especially, it was found that the catalyst had a profound effect on the graphitic and amorphous structures of the ion-irradiated membrane. Finally, we concluded that the amorphous structure in the membrane had an influence on the gas permeability and that the graphitic structure formed a barrier to the gas permeability and had an influence on the gas selectivity.