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 CO2 separation with amino groups serving as reactive CO2 carriers. Herein, to further enhance the CO2-facilitated transport effect of polyamide membrane, Zn(NO3)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(NO3)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 CO2 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 CO2/N2 and CO2/CH4 selectivity of 106.7 and 55.2, which increase, respectively, by 75.2% and 99.3% without compromising CO2 permeance in contrast with pristine polyamide membrane.