Probing the sensing potential of Nb- and Mo-based MXene nanosheets and their heterostructures for air pollutants: a DFT insight.

In this study, we utilized density functional theory (DFT) with plane-wave calculations to investigate the gas-sensing capabilities of Mo- and Nb-based MXene nanosheets, including NbC, NbN, MoC, and MoN, as well as their heterostructures (NbMoC and NbMoN). We focused on assessing their effectiveness in detecting hazardous airborne gases, such as carbon monoxide (CO) and nitrogen monoxide (NO). The adsorption energy, charge transfer, work function, and electronic properties of the nanosheets and their heterostructures were examined to understand their adsorption behavior. Molecular dynamics and phonon calculations confirmed the thermal and mechanical stability of the nanosheets, with NbMoC being more stable than NbMoN. The band structures and density of states (DOS) indicate the metallic behavior of the nanosheets. CO and NO were adsorbed on NbC, with adsorption energies of -3.014 and -4.479 eV, respectively. A similar adsorption phenomenon was found for NbN. The adsorption of CO and NO on MoC occurred with adsorption energies of -2.456 and -2.984 eV, respectively. For heterostructures, gas molecules were adsorbed on the Mo and Nb sites of the nanosheets, with the Nb site being more favorable. Therefore, all MXenes exhibit strong sensitivity towards gas molecules, high interaction properties in the chemisorption range, short adsorption distance, and a significant amount of charge transfer to the gases. Although MoN interacts with gas molecules at exceptionally high adsorption energies, it is unsuitable for gas adsorption because of its high recovery time and high structural deformation upon adsorption. Therefore, all nanosheets, except for MoN, were considered promising candidates for detecting CO and NO gas molecules.