posted on 2021-11-30, 16:03authored byYu Fu, Yue Wu, Shuhui Chen, Wenxiang Zhang, Ying Zhang, Tong Yan, Bolun Yang, Heping Ma
Ionic covalent organic frameworks
(COFs) consisting of an anionic
or cationic skeleton and corresponding counterions have demonstrated
great potential in many application fields such as ion conduction,
molecular separation, and catalysis. However, arranging anionic and
cationic groups into the same COF to form zwitterionic materials is
still unexplored. Herein we design the synthesis of three zwitterionic
COFs as attractive porous hosts for SO2/CO2 separation
and anhydrous proton conduction. The separated cationic and anionic
groups in zwitterionic COFs’ channels can act as two different
polar sites for SO2 adsorption, allowing zwitterionic COFs
to achieve a high SO2 adsorption capacity (216 mL/g, 298
K) and impressive SO2/CO2 selectivity (118,
298 K). Furthermore, after loading with triazole/imidazole, the zwitterionic
groups in COFs’ channels can induce complete proton carrier
deprotonation, producing more freely migrating protons. The free protons
migrate along a continuous hydrogen-bonding network in zwitterionic
COFs’ channels, leading to outstanding anhydrous proton conductivity
up to 4.38 × 10–2 S/cm, which is much higher
than other N-heterocyclic-doped porous materials under anhydrous conditions.
Proton dissociation energy calculations combined with frequency-dependent
dielectric analysis give insight into the role of zwitterionic COFs
for proton conductivity. Our work provides the possibility to design
well-defined zwitterionic frameworks for gas separation and ion conduction.