Facilitated transport membranes by incorporating graphene nanosheets with high zinc ion loading for enhanced CO2 separation

In this study, a novel kind of facilitated transport membrane was prepared by incorporating zinc ion-modified graphene (GO-DA-Zn 2+ ) nanosheets into a poly(ether-block-amide) (Pebax) matrix. Graphene oxide (GO) nanosheets were modified with zinc ion (Zn 2+ ) by using dopamine-mediated complexation reaction. The CO 2 separation properties of the facilitated transport membrane were evaluated using CO 2 /CH 4 mixture as model system. The GO-DA-Zn 2+ nanosheets played an important role in enhancing membrane performance. First, the high zinc ion loading (34.2   wt% of the nanosheets) could enhance the facilitated transport of CO 2 based on π-complexation mechanism, leading to a higher CO 2 permeability and selectivity. Second, the incorporation of graphene nanosheets with high aspect ratio rendered more tortuous gas transport channels, which was favorable for hindering the penetration of CH 4 with larger molecular size and thus enhancing the CO 2 /CH 4 selectivity. Third, the fractional free volume of hybrid membrane was much elevated, also leading to higher CO 2 permeability. The optimum separation properties of GO-DA-Zn 2+ incorporated Pebax membranes were achieved with a CO 2 permeability of 137.9   Barrer and a CO 2 /CH 4 selectivity of 30.6, which were 49% and 78% higher than those of pristine Pebax membrane.