Adsorption of Toxic Gases on Transition-Metal-Doped Janus MoSTe Monolayers: A First-Principles Study

Toxic gases such as SO2, CO, H2S, NO2, and NH3 released from industrial processes pose severe threats to human health and the environment, necessitating the development of highly sensitive gas-sensing materials. Two-dimensional Janus MoSTe has attracted attention for its asymmetric structure and tunable electronic properties, yet its potential for gas detection remains largely unexplored, particularly when functionalized with transition metal dopants. In this work, first-principles calculations based on density functional theory are employed to systematically investigate the gas adsorption properties of monolayer MoSTe doped with six transition metals (Ru, Rh, Pd, Os, Ir, Pt). The adsorption energies, electronic band structures, density of states, charge density differences, and recovery times are analyzed to evaluate the sensing performance. The results demonstrate that transition metal doping transforms the weak physisorption on pristine MoSTe into strong chemisorption, with adsorption energies ranging from -0.791 to -2.382 eV. Notably, Ir-MoSTe exhibits the highest sensitivity toward SO2 (-1.221 eV), Ru-MoSTe toward CO (-2.102 eV), and Os-MoSTe toward H2S, NO2, and NH3. While such strong chemisorption guarantees ultrahigh sensitivity, it concurrently increases the energy barrier for room-temperature desorption. Consequently, this study proposes that transition-metal-doped Janus MoSTe is highly suitable either as a highly efficient toxic gas scavenger or as a thermally activated gas sensor that requires moderately elevated temperatures for rapid recovery.