DFT study of NH3 adsorption on 2D monolayer MXenes (M2C, M = Cr, Fe) via oxygen functionalization: Suitable materials for gas sensors

This work deals with the kind of the interaction of NH3 molecules adsorbed on the MXene layers. The adsorption energies of NH3 on the surface of MXenes (M2C, M = Cr and Fe) and their oxygen-functionalized forms (OMXenes or M2CO2) were calculated by using the density functional theory. DFT-D4 calculations have revealed that the on-top sites are initiated for adsorption of NH3 on M2C and M2CO2. For the reaction on Cr2CO2, the Ead is found to be -0.29 eV lower than Cr2C and also the same tendency was achieved in Fe2C and its O-terminated MXene. This suggests that the molecule will strongly adsorb on Cr2C than its O-terminated surface. Bader charge analysis in terms of the induced net charges on M2C MXenes suggests that electron density distribution between N of NH3 (negatively charged) and the Cr/Fe (positively charged) surface would play a key role in the adsorption. Furthermore, DOS calculations reveal that the electrical conducting behaviour and magnetic nature of MXenes make them suitable for gas sensors applications.