Pristine and doped MoS 2 monolayers as potential HCN gas sensors: a DFT study

Abstract Two-dimensional transition metal dichalcogenides are promising sensing materials due to their tunable properties. Here, density functional theory is used to investigate hydrogen cyanide (HCN) adsorption on pristine and doped MoS 2 monolayers (X–MoS 2 , X = P, N, Si, Al, B, and Cl). Most dopants lead to weak physisorption with ultrafast recovery, while Al–MoS 2 exhibits strong chemisorption with an adsorption energy of − 1.459 eV, resulting in an impractically long recovery time. Among the single-doped systems, Si–MoS 2 shows a favorable microsecond-scale response. To overcome the recovery-time limitations associated with strong adsorption, dopant concentration effects are examined by substituting two and three sulfur atoms with P, Si, and Al. A non-monotonic trend is observed, wherein double doping enhances the adsorption strength, while symmetric triple doping weakens the interaction, enabling recovery-time tuning at room temperature. In particular, 2Si–MoS 2 exhibits a recovery time of 15.48 min along with strong electronic sensitivity, whereas 3Al–MoS 2 achieves balanced adsorption with a recovery time of 3.24 ms, accompanied by significant work-function modulation and enhanced electron emission current density. This dopant-engineering approach provides an intrinsic and safer alternative to temperature- or field-driven desorption strategies, offering practical design guidelines for chemiresistive, electrochemical, and ultraviolet-based HCN sensing using MoS 2 .