One step synthesis of flexible covalent organic Frameworks in water for efficient separation of CO2/CH4

Flexible COFs have attracted significant interest due to the flexibility conferred by single bonds. However, their considerable degrees of freedom and varying conformations hinder the attainment of appropriate bonding orientations during polymerization and crystallization, thus complicating the synthesis of flexible COFs and limiting their applications. Two flexible C-N-linked COFs are presented for the first time using ultrasound-assisted methods in water with non-toxic organic solvents within a duration of 60 min. The synthesized COFs exhibit high CO2 capture capacity and excellent CO2/CH4 separation performance. Dynamic breakthrough experiments revealed that the two flexible COFs possess controllable CO2/CH4 separation performance, demonstrating the ability to remove trace amounts of CO2 (1%) from CO2/CH4 mixtures. At 273 K, with a purity exceeding 99.9% can be obtained in a single step, yielding CH4 amounts of 1.27 and 1.65 mmol/g within 115.3 s and 129.5 s, respectively. Compared with their corresponding rigid COFs, this increases by 36% and 34%, respectively. The simulation results of GCMC and DFT calculations indicate that the strong affinity between TAT-TB-COF-H and CO2 is the reason for its excellent CO2/CH4 separation performance. The remarkable CO2 adsorption and CO2/ CH4 separation performance of the synthesized flexible C-N-linked COFs support ongoing efforts to develop effective, scalable, and environmentally friendly solutions for CO2 capture and natural gas purification.