DFT insights into the gas sensing performance of M2X (M = Zr, Hf; X = C, N) MXenes and their Janus derivatives for toxic gases

Abstract

Widespread air pollution caused by toxic, flammable, and hazardous gases has been linked to numerous health issues. Gas sensors play a crucial role in the detection and monitoring of these harmful substances. In this study, Zr and Hf-based carbide and nitride MXenes (Zr₂C, Zr₂N, Hf₂C, and Hf₂N) and their Janus structures (ZrHfC and ZrHfN) were investigated for their sensing performance towards the toxic CO, NO, NO₂, and SO₂ gas molecules using density functional theory (DFT). The adsorption behavior in terms of adsorption energy, charge transfer, recovery time, electronic properties in terms of band structures, density of states (DOS), and work function were examined to understand the sensing behavior of the nanosheets. Chemisorption interactions were found for all of the complexes except CO and SO₂ adsorption on ZrHfC. Favorable adsorption characteristics were observed for the CO and NO gases on all the nanosheets. The adsorption energies ranged from −1.65 to −3.37 eV for CO and −4.42 to −5.32 eV for NO, with corresponding Mulliken charge transfers of −0.152 to −1.00e and −0.172 to −1.038e, respectively. But in the case of NO₂ and SO₂, very high adsorption characteristics with high deformation of the gases in the complexes were found, which leads to unfavorable adsorption performances. Furthermore, the work functions of the nanosheets varied during the adsorption of gas molecules. Thus, all calculations indicate that all six nanosheets can be useful for monitoring CO and NO.