Zn ion-modulated polyamide membrane with enhanced facilitated transport effect for CO2 separation

Polyamide membrane, fabricated via interfacial polymerization process, is a typical class of facilitated transport membrane for CO 2 separation with amino groups serving as reactive CO 2 carriers. Herein, to further enhance the CO 2 -facilitated transport effect of polyamide membrane, Zn(NO 3 ) 2 is directly introduced into aqueous triethylenetetramine phase for constructing Zn-N coordination polyamide membrane taking advantage of the coordination interaction between Zn ions and amino groups from triethylenetetramine. The good solubility of Zn(NO 3 ) 2 in aqueous amine solution and moderate coordinative ability of Zn ions are beneficial to a uniform distribution of Zn in polyamide layer. The coordination of N from triethylenetetramine monomer to Zn ion centre produces more tertiary amino groups and free amino groups with stronger affinity to CO 2 in Zn-N coordination membrane for enhancing the facilitated transport effect. Additionally, the Zn-N coordination interaction generates smoother surface of membranes when sufficient Zn ions are introduced. The membrane with 0.1 wt% of Zn ions in aqueous phase exhibits the highest CO 2 /N 2 and CO 2 /CH 4 selectivity of 106.7 and 55.2, which increase, respectively, by 75.2% and 99.3% without compromising CO 2 permeance in contrast with pristine polyamide membrane.