Facilitated transport membranes by incorporating self-exfoliated covalent organic nanosheets for CO2/CH4 separation

Two-dimensional (2D) covalent organic nanosheets (CONs) present versatile 2D materials, which hold great promise in mixed matrix membranes. The facile synthesis of CONs for the fabrication of mixed matrix membranes represents the development trend. Herein, mixed matrix membranes with facilitated transport ability were prepared based on self-exfoliated covalent organic nanosheets (CONs) and poly(ether-block-amide) (Pebax® MH 1657) matrix. The self-exfoliated TpDT CONs were facilely synthesized via Schiff base condensation reaction between 1,3,5-Triformylphloroglucinol (Tp) and 3, 5-diamino-1,2,4-triazole (DT). Abundant amine groups on TpDT CONs skeleton served as facilitated transport carriers to promote the transport of CO2 by reversible nucleophilic addition reactions. And the highly ordered channels of TpDT CONs allowed the rapid transportation of CO2 molecules to reach the facilitated transport carriers. Moreover, the incorporated TpDT CONs disturbed the packing of the Pebax chains by the intervention effects and increased the chain mobility. The facilitated transport carriers from TpDT CONs and the optimized structure endowed the as-prepared membranes with elevated permeance and selectivity. Specially, the Pebax-TpDT/PVDF membranes with 1 wt% TpDT CONs achieved an optimum CO2/CH4 separation performance with a separation factor of 36.0 and a CO2 permeance of 142.3 GPU, which were increased by 68% and 131%, respectively, compared with the pristine Pebax membrane.