Electronic origin of gas selectivity on Co/Fe-modified WS2 monolayers for NO2 sensing

Abstract

Industrial emissions of NO₂ and H₂S are exacerbating the global environmental crisis. Abundant and cost-effective transition metals Co and Fe can precisely modulate the electronic structure of WS₂, enabling efficient detection of these pollutants. This study focuses on a typical industrial exhaust environment containing NO₂, H₂S, and H₂O, introducing Co and Fe into WS₂ monolayers through both doping and loading strategies, and performing systematic calculations using density functional theory. The modified WS₂ maintains structural integrity, with changes in cohesive energy of within 5%. Preferential adsorption-oriented high-activity sites can be identified using electrostatic potential and work function maps. Adsorption energies and distances together indicate that supported Co/Fe–WS₂ exhibits superior performance compared to doped configurations. Notably, density of states analysis reveals that the modification method and metal type determine gas selectivity. In the coexistence of NO₂, H₂S, and H₂O, supported Co/Fe–WS₂ shows a significant preference for NO₂, whereas doped Co/Fe–WS₂ exhibits non-selective adsorption toward both NO₂ and H₂S. Crystal orbital Hamiltonian population and d-band center analysis quantitatively reveal the electronic origin of this selectivity. The orbital matching between Co/Fe loading sites and NO₂ is optimal, achieving a better balance between adsorption efficiency and specificity. Gibbs free energy calculations further confirm that supported Co/Fe–WS₂ has a wider temperature range for target gas NO₂, extending up to 1000 K. In addition, its adsorption of H₂O is extremely weak, demonstrating high moisture resistance. Overall, Co/Fe-loaded WS₂ monolayers demonstrate potential in industrial exhaust gas detection and environmental monitoring. The theoretical insights from this study support the design of high-performance NO₂ gas sensors.