Detection of common harmful gases at S-sites of Ti-doped monolayer MoS₂: a first-principles DFT study

CO, CO₂, NO, and NO₂ are major air pollutants that pose significant threats to ecosystems and human health. Therefore, the development of efficient detection and adsorption technologies is of great importance for environmental protection and public health. MoS₂ has shown promising potential in the field of gas sensing. However, its intrinsic chemical inertness severely limits the detection performance and adsorption efficiency toward CO, CO₂, NO, and NO₂. Consequently, surface modification strategies, such as heteroatom doping, are highly necessary to enhance its gas-sensing properties. This work focuses on the S-site Ti-doped MoS₂ system and systematically investigates its adsorption performance towards the four typical hazardous gases. Using density functional theory (DFT) calculations, we comprehensively analyze the optimal adsorption configurations, adsorption energies, charge transfer properties, density of states (DOS), and band structures of the Ti-MoS₂ system interacting with the target gases. The results demonstrate that Ti doping can effectively regulate the electronic structure and surface activity of MoS₂, thereby significantly strengthening its adsorption toward the target gases. This study clearly reveals the microscopic gas-sensing mechanism of S-site Ti-doped MoS₂, providing important theoretical basis for the design of high-performance two-dimensional transition metal dichalcogenide (TMDC)-based gas sensors and expanding the application prospects of MoS₂ materials in environmental gas detection.