DFT-Based Insights into the Functionalization of MoSe ₂ Monolayers via Substitutional Doping for Enhanced Gas Detection

To enhance safety in industrial processes and prevent dangerous exposures to hazardous gases such as H2, H2S, and HCN, early detection and monitoring are essential. Using Density Functional Theory, we investigated the D-MoSe2 (D-Pt, Ir, and Os) monolayers as sensing materials and analyzed their structures, electronic properties, and gas-sensing behaviors. The absence of imaginary phonon bands confirms the dynamical stability of the substitutionally doped monolayers. Their band gaps decrease as new energy states form, and charges are redistributed, improving the surface for better gas adsorption. The Ir-MoSe2 monolayer interacts highly with all three gases and yields adsorption energies of −0.59 eV for H2, −1.17 eV for H2S, and −1.01 eV for HCN. The substantial charges donated from the gas to the material are 0.094, 0.267, and 0.134 e. Followed by which the Pt-MoSe2 monolayer also chemically interacts with H2S and HCN gases with significant charge transfer and adsorption energies. The doped monolayers exhibit profound changes in their sensing and electronic properties, as observed through changes in band structure, density of states, electron density differences, and electron localization function-based interactions. The work function changes for Pt-MoSe2 indicate selective detection (−0.27 and −0.34 eV), and for the Ir-MoSe2 monolayer, it shows nearly identical changes (−0.35 and −0.34 eV) for H2S and HCN gases. The Pt-MoSe2 monolayer releases HCN gas within 12.79 s at 323 K, enabling reliable, repeatable sensing. Also, the Ir-MoSe2 monolayer recovers HCN gas in 5.32 s at 400 K. Therefore, the Pt- and Ir-MoSe2 monolayers are acceptable choices for efficient gas-sensing applications, enabling the rational design of a nanosensor with sensitive and selective detection of targeted hazardous gases.