Controlled Pore Sizes in Monolayer C₂N Act as Ultrasensitive Probes for Detection of Gaseous Pollutants (HF, HCN, and H₂S)

Porous two-dimensional monolayers have gained interest both in theoretical and experimental research because of their controlled pore size and evenly distributed holes within the basal plane. Herein, we have investigated the efficient trapping of three pollutants (HF, HCN, and H₂S) on the recently synthesized porous two-dimensional nitrogeneted holey carbon (C₂N-h2D) monolayer using periodic density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. The differential binding positions/orientations of HF, HCN, and H₂S in the cavity of C₂N depend on their adsorption energy and charge transfer efficiency. H₂S serves as a charge donor while HF and HCN act as charge acceptors. Our AIMD simulations demonstrate that the C₂N monolayer is thermally stable at room temperature. Adsorption occurs through physisorption, and no chemical bond is formed between the molecule and the C₂N surface irrespective of the site of interaction. Electrostatic interactions and hydrogen bonding facilitate strong noncovalent interactions between the polar pollutants and C₂N. I-V characteristics of the C₂N monolayer in the presence of the adsorbed molecules show an increase in current for H₂S at a bias of 1.0 V. However, for acceptor molecules, it shows a decrease (HF, bias = 3.0 V and HCN, bias = 2.5 V). Such unique sensitivity of C₂N toward donor/acceptor molecules advocates its application for gas sensing applications.