Nitrogen configuration dependent gas sensing performance based on nitrogen contained covalent organic polymers and frameworks

Gas sensing was a very important strategy to detect toxic and harmful gases, which was discharged into atmosphere. N-contained groups had been confirmed an important adsorption sites for target molecules in gas sensing process. Herein, we designed four N-contained groups in different configurations, including primary amine, secondary amine, tertiary amine and quaternary ammonium, to verify their difference in sensing performance. These four N-contained groups were embedded in four covalent organic polymers/frameworks through reasonable designation of building blocks. The sensing results indicated that primary amine, secondary amine and tertiary amine were excellent NH3 adsorption sites and beneficial for NH3 sensing. For 100 ppm NH3, the response value, response/recovery time were - 62%, 24 s/202 s for Amino-COP sensor, were - 51%, 18 s/173 s for Caz-COP sensor, and were - 76%, 19 s/206 s for CTF sensor at room temperature. The estimated LOD were 10 ppb for Amino-COP, 76 ppb for Caz-COP and 7.5 ppb for CTF, respectively. In contrast, quaternary ammonium was mainly NO2 adsorption site and could be applied in NO2 sensing. The response value, response/recovery time were - 76%, 76 s/264 s for Vio-COF to 100 ppm NO2. And the low LOD of 1.1 ppb was observed on Vio-COF sensor. Density functional theory (DFT) calculation and in-situ UV-Vis experiments confirmed that NH3 was interacted with primary amine, secondary amine, and tertiary amine through hydrogen bonding ways, while NO2 interacted with quaternary nitrogen atoms through coordination.