Exploring the sensing properties of Janus ScSTe, TiSTe, and ZrSTe nanosheets for nitrogen based toxic gases via DFT

In the current scenario, nitrogen-based gases such as nitric oxide (NO), nitrogen dioxide (NO₂), and ammonia (NH₃) are bringing about serious threats to human health and the ecosystems, even at minimal concentrations, making the purification of these gases vital for environmental safety. In this investigation, density functional theory (DFT) calculations were carried out to examine the gas sensing properties and adsorption behavior of ScSTe, TiSTe, and ZrSTe nanosheets towards the NO, NO_2, and NH₃ gas molecules. All the nanosheets exhibit metallic behavior, with the dominant contribution arising from the p orbitals in ScSTe, and from the d orbitals in TiSTe and ZrSTe. To identify the most stable gas adsorption site, two sites (S site and Te site) on the nanosheets were considered. Our adsorption energy calculations indicate weak physisorption across all the nanosheets. The adsorption energy ranges for NO, NO₂, and NH₃ gas molecules are from - 0.080 eV to - 0.406 eV for ScSTe, - 0.144 eV to - 0.287 eV for TiSTe, and - 0.103 eV to - 0.354 eV for ZrSTe. Among all nanosheets, the S site exhibits better adsorption energies with NO and NH_3, and the Te site for NO₂ gas molecules. During the interaction, the gas molecules generally donate charge to the nanosheets, except for NO₂, which tends to withdraw charge due to the presence of two electronegative oxygen atoms. A low recovery time was observed for all gas-nanosheet interactions, which is favorable for gas sensing applications. Among the materials, ScSTe shows stronger interaction with NO and NH₃, while ZrSTe is more responsive to NO₂.