Hazardous gas adsorption and sensing by pristine and Pd/Mo-decorated TiS2: a first-principles study

Abstract

The rapid expansion of industrial activities necessitates the development of cost-effective and highly sensitive gas sensors for the detection of hazardous gases such as NO₂, SO₂, NO, and H₂S. Two-dimensional TiS₂ has attracted considerable attention due to its tunable electronic properties and large surface area. However, its inherently weak interaction with gas molecules limits its practical sensing performance. In this study, first-principles density functional theory (DFT) calculations within the CASTEP framework are employed to systematically investigate the adsorption and sensing characteristics of pristine, palladium (Pd), and molybdenum (Mo) decorated TiS₂ monolayers. Pristine TiS₂ exhibits physisorption for SO₂, NO₂, and H₂S, with chemisorption observed only for NO. In contrast, Pd and Mo decoration (Pd/Mo/TiS₂) significantly enhance the adsorption capability of TiS₂, leading to stronger chemisorption with higher adsorption energies, shorter adsorption distances, and pronounced charge transfer. Mo/TiS₂, in particular, demonstrates strong interactions with adsorption energies ranging from −1.01 eV to −3.421 eV. Electronic structure analysis reveals that NO₂ and NO adsorption on Mo/TiS₂ induces a transition to metallic behavior, resulting in markedly enhanced conductivity and superior sensitivity (392.732 at room temperature), surpassing both pristine and Pd/TiS₂. Recovery time analysis shows that Mo/TiS₂ undergoes extremely slow desorption, with values of 5.544 × 10³⁷ s for NO₂ and 6.8 × 10⁴⁵ s for NO under ambient conditions. In contrast, Pd/TiS₂ demonstrates more practical recovery behavior, with SO₂, NO, and H₂S desorbing within 8.598 × 10⁻³, 0.003, and 65.08 s, respectively. Work function analyses further confirm that Pd and Mo decoration improve charge transport efficiency and enhance sensor selectivity. These results highlight Pd/Mo-decorated TiS₂ as promising candidates for high-performance gas sensors in industrial applications.