Recent reports have raised exciting prospects for the use of C 3 N monolayers exhibiting excellent adsorptive properties in nanodevice applications. In this study, we carried out first-principle calculations to investigate the adsorption of NO 2 , NO, CO, HCN, NH 3 , CO 2 , H 2 , N 2 , CH 4 , H 2 O, O 2 , and N 2 O gas molecules on a C 3 N monolayer as well as its potential applications in gas sensor devices. Our results reveal that the chemisorption of NO 2 can significantly influence the

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... ronic properties of the C 3 N monolayer (e.g., changing semiconducting behavior to conducting behavior). In contrast, physisorption of the other gas molecules had little effect on the electronic properties of the C 3 N monolayer. These results suggest that the C 3 N monolayer is much more sensitive and selective to NO 2 than to the other gases. The recovery time of NO 2 at T = 300 K is only 0.62 s. Moreover, the optical properties of the C 3 N monolayer can be modified as a result of the adsorption of different molecules, especially the NO 2 molecule. Thus, the C 3 N monolayer is a promising and desirable candidate for use as a suitable material in gas sensors for NO 2 detection.