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 (O-MXenes 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 E_ad 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.