Dual polarization strategy to enhance CH4 uptake in covalent organic frameworks for coal-bed methane purification

The purification of low-grade coal-bed methane is extremely important, but challenging, due to the very similar physical properties of CH4 and N2. Herein, we proposed a dual polarization strategy by employing triazine and polyfluoride sites to construct polar pores in COF materials, achieving the efficient separation of CH4 from N2. As expected, the dual polarized F-CTF-1 and F-CTF-2 exhibit higher CH4 adsorption capacity and CH4/N2 selectivity than CTF-1 and CTF-2, respectively. Especially, the CH4 uptake capacity and CH4/N2 selectivity of F-CTF-2 is 1.76 and 1.42 times than that of CTF-2. This work not only developed promising COF materials for CH4/N2 separation, but also provided important guidance for the separation of other adsorbates with similar properties.